diff --git a/swh/model/cli.py b/swh/model/cli.py
--- a/swh/model/cli.py
+++ b/swh/model/cli.py
@@ -169,6 +169,8 @@
     \b
     https://docs.softwareheritage.org/devel/swh-model/persistent-identifiers.html
 
+    Tip: you can pass "-" to identify the content of standard input.
+
     \b
     Examples:
 
@@ -189,7 +191,7 @@
 
     """  # NoQA  # overlong lines in shell examples are fine
     if not objects:
-        objects = ["-"]
+        raise click.UsageError("no object given")
 
     if verify and len(objects) != 1:
         raise click.BadParameter("verification requires a single object")
diff --git a/swh/model/tests/test_cli.py b/swh/model/tests/test_cli.py
--- a/swh/model/tests/test_cli.py
+++ b/swh/model/tests/test_cli.py
@@ -38,7 +38,7 @@
         """identify file content"""
         self.make_contents(self.tmpdir_name)
         for _, content in self.contents.items():
-            result = self.runner.invoke(cli.identify, input=content["data"])
+            result = self.runner.invoke(cli.identify, ["-"], input=content["data"])
             self.assertPidOK(result, "swh:1:cnt:" + hash_to_hex(content["sha1_git"]))
 
     def test_directory_id(self):