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I've read the thread about editing my Profile, but when I go into my Control Panel and click Edit Profile, I find nothing there that lets me add a signature. Am I missing something?
Click Control Panel, on the left there should be a link titled Edit Signature.
Although I recall reading that you need at least 10 posts are needed before that feature is available. The number might be higher than 10, I am not sure.
10 post requirement for signature is a nice way to fish out spammers. They'll either rush to increase their post-count or make a fake signature directly in their posts.