How long do you have to be a member before you can add a sig?

Title says it all.

Moved from “Misc: > Off-topic Chat” to “Support > Blender Artists Website Support”

As noted in the Forum FAQ, new members to the forum have restricted permissions. Signatures are among those restrictions. After you have 10 posts go through the moderation queue, the restrictions will be lifted.

Do also note that the FAQ also covers our rules regarding signatures. Please pay attention to that section as well.