diff --git a/doc/command-line.md b/doc/command-line.md
index eda5b2ac2c..640ff9c9a5 100644
--- a/doc/command-line.md
+++ b/doc/command-line.md
@@ -1041,6 +1041,9 @@ superkingdom, phylum, class, order, family, genus, and species.
 to ignore case and `-v` to output only taxonomic lineages that do
 _not_ match the pattern.
 
+Note: `tax grep` only searches taxonomic ranks, not identifier strings.
+Use `sig grep` to search for identifiers in sketch collections.
+
 Currently only CSV output (optionally gzipped) is supported; use `sourmash tax prepare` to
 convert CSV output from `tax grep` into a sqlite3 taxonomy database.
 
diff --git a/src/sourmash/cli/tax/grep.py b/src/sourmash/cli/tax/grep.py
index 003c152dc1..9aa5db3b89 100644
--- a/src/sourmash/cli/tax/grep.py
+++ b/src/sourmash/cli/tax/grep.py
@@ -1,4 +1,4 @@
-"""search taxonomies and output picklists.."""
+"""search taxonomies and output picklists."""
 
 usage="""
 
@@ -9,6 +9,9 @@
 It creates new files containing matching taxonomic entries; these new
 files can serve as taxonomies and can also be used as picklists.
 
+`tax grep` only searches taxonomic ranks, not identifier strings.
+Use `sig grep` to search for identifiers in sketch collections.
+
 Please see the 'tax grep' documentation for more details:
   https://sourmash.readthedocs.io/en/latest/command-line.html#sourmash-tax-grep-subset-taxonomies-and-create-picklists-based-on-taxonomy-string-matches
 """