[Lara]

You just need to "Save Signature" after you've added it into the box in your Edit Signature area in your User CP


There is Thread Display Options under Edit Options in the Control Panel.
You also need to make sure that you have checked "Show Signatures".

After making sure that is checked, one needs to "Save Changes" at the bottom of that page.

Visible Post Elements
You have the option to show or hide various elements of messages, which may be of use to users on slow internet connections, or who want to remove extraneous clutter from posts.
Show Signatures
Show Avatars
Show Images (including attached images and images in [IMG] code)

After you've done all that, make a post and it should show up.