This version adds an "Enable signature once" permission to decide if the user should benefit from add-on.
You will almost certainly want to enable it for all users, but it gives you the flexibility to turn it off for others (e.g. discouraged).
Also fixes an issue where a moderated or deleted post that wasn't actually visible would have the signature on, and all other posts by the user would have it removed.
Can't seem to get this working and I can't figure out why. :/
Just installed. Did not seem to do anything at least for existing threads. Then realized it needs to also be set to on for each user group.