How do I add my signature?

I want to add my signature which shows on the bottom of every posts.

I searched "signature" on the FAQ of this forum, it says:

"How do I set signatures, avatars and profile pictures?

You can set and change your signature, avatar and profile picture in the User Control Panel (providing the administrator has made these options available).

For signatures, click on 'Edit Signature' under the 'Settings and Options' area of the navigation bar within the User CP."

While, I can't find any "Edit Signature" under the 'Settings and Options' area of the navigation bar within the User CP." What's the problem? Anyone tell me?