+Otherwise just the SHA1 object name of the commit object is
+written (i.e. an lightweight tag).
+
+A GnuPG signed tag object will be created when `-s` or `-u
+<key-id>` is used. When `-u <key-id>` is not used, the
+committer identity for the current user is used to find the
+GnuPG key for signing.