If you already saw where to edit in a signature and it would not save, it may not be within signature guidelines...
Try PMing a Moderator for help.
So...
Near the top on the left you see your Avatar and screen name?
Click on "Settings" (next to the gear) > click on "Edit Signature" > Use the editor box... It's very similar to the Reply box.
View attachment 90311
As you can tell... It is a WYSIWYG editor *What You See Is What You Get*
When you have it the way you like, click Save Signature.