diff --git a/src/sourmash/__init__.py b/src/sourmash/__init__.py
index 0077ea199c..9f6e98cd91 100644
--- a/src/sourmash/__init__.py
+++ b/src/sourmash/__init__.py
@@ -5,6 +5,7 @@
 import re
 import math
 import os
+from deprecation import deprecated
 
 from ._lowlevel import ffi, lib
 
@@ -30,13 +31,63 @@
 MAX_HASH = get_minhash_max_hash()
 
 from .signature import (
-    load_signatures,
+    load_signatures as load_signatures_private,
     load_one_signature,
     SourmashSignature,
     save_signatures,
 )
 
-from .sbtmh import load_sbt_index, search_sbt_index, create_sbt_index
+@deprecated(deprecated_in="3.5.1", removed_in="5.0",
+            current_version=VERSION,
+            details='Use load_file_as_signatures instead.')
+def load_signatures(*args, **kwargs):
+    """Load a JSON string with signatures into classes.
+
+    Returns list of SourmashSignature objects.
+
+    Note, the order is not necessarily the same as what is in the source file.
+
+    This function has been deprecated as of 3.5.1; please use
+    'load_file_as_signatures' instead. Note that in 4.0, the 'quiet' argument
+    has been removed and the function no longer outputs to stderr.
+    Moreover, do_raise is now True by default.
+    """
+    return load_signatures_private(*args, **kwargs)
+
+from .sbtmh import load_sbt_index as load_sbt_index_private
+from .sbtmh import search_sbt_index as search_sbt_index_private
+
+@deprecated(deprecated_in="3.5.1", removed_in="5.0",
+            current_version=VERSION,
+            details='Use load_file_as_index instead.')
+def load_sbt_index(*args, **kwargs):
+    """Load and return an SBT index.
+
+    This function has been deprecated as of 3.5.1; please use
+    'load_file_as_index' instead.
+    """
+    return load_sbt_index_private(*args, **kwargs)
+
+
+@deprecated(deprecated_in="3.5.1", removed_in="5.0",
+            current_version=VERSION,
+            details='Use the new Index API instead.')
+def search_sbt_index(*args, **kwargs):
+    """\
+    Search an SBT index `tree` with signature `query` for matches above
+    `threshold`.
+
+    Usage:
+
+        for match_sig, similarity in search_sbt_index(tree, query, threshold):
+           ...
+
+    This function has been deprecated as of 3.5.1; please use
+    'idx = load_file_as_index(...); idx.search(query, threshold=...)' instead.
+    """
+    return load_sbt_index_private(*args, **kwargs)
+
+from .sbtmh import create_sbt_index
 from . import lca
 from . import sbt
 from . import sbtmh
diff --git a/src/sourmash/commands.py b/src/sourmash/commands.py
index 73b39adef8..415e6e99ce 100644
--- a/src/sourmash/commands.py
+++ b/src/sourmash/commands.py
@@ -8,7 +8,8 @@
 
 import screed
 from .compare import compare_all_pairs, compare_serial_containment
-from . import MinHash, load_sbt_index, create_sbt_index
+from . import MinHash
+from .sbtmh import load_sbt_index, create_sbt_index
 from . import signature as sig
 from . import sourmash_args
 from .logging import notify, error, print_results, set_quiet
diff --git a/src/sourmash/index.py b/src/sourmash/index.py
index b67c6d4707..8dd4069f04 100644
--- a/src/sourmash/index.py
+++ b/src/sourmash/index.py
@@ -145,7 +145,7 @@ def save(self, path):
     @classmethod
     def load(cls, location):
         from .signature import load_signatures
-        si = load_signatures(location)
+        si = load_signatures(location, do_raise=True)
 
         lidx = LinearIndex(si, filename=location)
         return lidx
diff --git a/src/sourmash/lca/command_index.py b/src/sourmash/lca/command_index.py
index 2676e40bc3..d4febd4ae1 100644
--- a/src/sourmash/lca/command_index.py
+++ b/src/sourmash/lca/command_index.py
@@ -6,7 +6,7 @@
 import csv
 from collections import defaultdict
 
-from sourmash import sourmash_args, load_signatures
+from sourmash import sourmash_args
 from sourmash.sourmash_args import load_file_as_signatures
 from sourmash.logging import notify, error, debug, set_quiet
 from . import lca_utils
diff --git a/src/sourmash/signature.py b/src/sourmash/signature.py
index cac62fbc13..b067b7f0e7 100644
--- a/src/sourmash/signature.py
+++ b/src/sourmash/signature.py
@@ -222,7 +222,6 @@ def _detect_input_type(data):
 
 def load_signatures(
     data, ksize=None, select_moltype=None, ignore_md5sum=False, do_raise=False,
-    quiet=False
 ):
     """Load a JSON string with signatures into classes.
 
@@ -248,8 +247,6 @@ def load_signatures(
 
     input_type = _detect_input_type(data)
     if input_type == SigInput.UNKNOWN:
-        if not quiet:
-            error("Error in parsing signature; quitting. Cannot open file or invalid signature")
         if do_raise:
             raise Exception("Error in parsing signature; quitting. Cannot open file or invalid signature")
         return
@@ -301,9 +298,6 @@ def load_signatures(
             yield sig
 
     except Exception as e:
-        if not quiet:
-            error("Error in parsing signature; quitting.")
-            error("Exception: {}", str(e))
         if do_raise:
             raise
 
diff --git a/src/sourmash/sourmash_args.py b/src/sourmash/sourmash_args.py
index 4bb537478b..258b99cee0 100644
--- a/src/sourmash/sourmash_args.py
+++ b/src/sourmash/sourmash_args.py
@@ -1,5 +1,5 @@
 """
-Utility functions for dealing with input args to the sourmash command line.
+Utility functions for sourmash CLI commands.
 """
 import sys
 import os
@@ -9,7 +9,7 @@
 
 import screed
 
-from sourmash import load_sbt_index
+from sourmash.sbtmh import load_sbt_index
 from sourmash.lca.lca_db import load_single_database
 import sourmash.exceptions
 
@@ -365,7 +365,7 @@ def _load_database(filename, traverse_yield_all, *, cache_size=None):
 
     # special case stdin
     if not loaded and filename == '-':
-        db = sourmash.load_signatures(sys.stdin, quiet=True, do_raise=True)
+        db = signature.load_signatures(sys.stdin, do_raise=True)
         db = list(db)
         loaded = True
         dbtype = DatabaseType.SIGLIST
@@ -376,7 +376,7 @@ def _load_database(filename, traverse_yield_all, *, cache_size=None):
         for thisfile in traverse_find_sigs([filename], traverse_yield_all):
             try:
                 with open(thisfile, 'rt') as fp:
-                    x = sourmash.load_signatures(fp, quiet=True, do_raise=True)
+                    x = signature.load_signatures(fp, do_raise=True)
                     siglist = list(x)
                     all_sigs.extend(siglist)
             except (IOError, sourmash.exceptions.SourmashError):
@@ -394,7 +394,7 @@ def _load_database(filename, traverse_yield_all, *, cache_size=None):
         # CTB: could make this a generator, with some trickery; but for
         # now, just force into list.
         with open(filename, 'rt') as fp:
-            db = sourmash.load_signatures(fp, quiet=True, do_raise=True)
+            db = signature.load_signatures(fp, do_raise=True)
             db = list(db)
 
         loaded = True
diff --git a/tests/test_sbt.py b/tests/test_sbt.py
index 1271c3b460..a825067cc0 100644
--- a/tests/test_sbt.py
+++ b/tests/test_sbt.py
@@ -9,7 +9,7 @@
 from sourmash.exceptions import IndexNotSupported
 from sourmash.sbt import SBT, GraphFactory, Leaf, Node
 from sourmash.sbtmh import (SigLeaf, search_minhashes,
-                            search_minhashes_containment)
+                            search_minhashes_containment, load_sbt_index)
 from sourmash.sbt_storage import (FSStorage, RedisStorage,
                                   IPFSStorage, ZipStorage)
 
@@ -775,7 +775,7 @@ def test_sbt_protein_command_index(c):
     c.run_sourmash('index', db_out, sigfile1, sigfile2,
                    '--scaled', '100', '-k', '19', '--protein')
 
-    db2 = sourmash.load_sbt_index(db_out)
+    db2 = load_sbt_index(db_out)
 
     sig1 = sourmash.load_one_signature(sigfile1)
     sig2 = sourmash.load_one_signature(sigfile2)
@@ -821,7 +821,7 @@ def test_sbt_hp_command_index(c):
     c.run_sourmash('index', db_out, sigfile1, sigfile2,
                    '--scaled', '100', '-k', '19', '--hp')
 
-    db2 = sourmash.load_sbt_index(db_out)
+    db2 = load_sbt_index(db_out)
 
     sig1 = sourmash.load_one_signature(sigfile1)
     sig2 = sourmash.load_one_signature(sigfile2)
@@ -867,7 +867,7 @@ def test_sbt_dayhoff_command_index(c):
     c.run_sourmash('index', db_out, sigfile1, sigfile2,
                    '--scaled', '100', '-k', '19', '--dayhoff')
 
-    db2 = sourmash.load_sbt_index(db_out)
+    db2 = load_sbt_index(db_out)
 
     sig1 = sourmash.load_one_signature(sigfile1)
     sig2 = sourmash.load_one_signature(sigfile2)
diff --git a/tests/test_sourmash.py b/tests/test_sourmash.py
index 40cc83ffb9..7fc2df5915 100644
--- a/tests/test_sourmash.py
+++ b/tests/test_sourmash.py
@@ -4121,6 +4121,12 @@ def test_do_sourmash_index_zipfile_append(c):
     first_half = testdata_sigs[:half_point]
     second_half = testdata_sigs[half_point:]
 
+    print(first_half)
+    print(second_half)
+
+    # should be no overlap
+    assert not set(first_half).intersection(set(second_half))
+
     with pytest.warns(None) as record:
         c.run_sourmash('index', '-k', '31', 'zzz.sbt.zip',
                        *first_half)
@@ -4138,7 +4144,8 @@ def test_do_sourmash_index_zipfile_append(c):
         c.run_sourmash('index', "--append", '-k', '31', 'zzz.sbt.zip',
                        *second_half)
     # UserWarning is raised when there are duplicated entries in the zipfile
-    assert not record
+    print(record)
+    assert not record, record
 
     print(c)
     assert c.last_result.status == 0
diff --git a/utils/check-tree.py b/utils/check-tree.py
index 4091c7ce84..12fc0190de 100644
--- a/utils/check-tree.py
+++ b/utils/check-tree.py
@@ -15,7 +15,7 @@ def main():
     p.add_argument('sbt')
     args = p.parse_args()
 
-    db = sourmash.load_sbt_index(args.sbt)
+    db = sourmash.sbtmh.load_sbt_index(args.sbt)
     threshold = THRESHOLD
 
     for leaf in db.leaves():