Lightweight Tags

Git supports two kinds of tags, both created using the "git tag" command: lightweight tags and tag objects. Lightweight tags have no authorship information, nor do they contain the date they were created or a message why, and hence are of limited use in the project history. For these reasons, lightweight tags are disallowed in GNOME git repositories.

The exact error message you get if you try to push a lightweight tag to GNOME repositories is:

You are trying to push the lightweight tag '$tagname'. You should use
a signed tag instead. See:

  http://live.gnome.org/Git/Help/LightweightTags

To fix this, you need to first delete your lightweight tag using:

git tag -d tagname

And then create a tag object using either "-a" or "-s" option to "git tag":

git tag -s tagname

The difference between -a and -s is that with -s, your GPG key is used to sign the tag. This is strongly recommended as it provides a strong cryptography proof that you made the tag, not anyone else using your name and email address.

See this page for more information.