if you got to settings, scroll bit down till you see My profile-edit profile-edit avatar-edit signature-...
Originally Posted by Murdoc1905
click on edit signature.
In the box that now shows up fill in
[_URL="http://myanimelist.net/animelist/Synaia"][_IMG]http://i.imgur.com/BIjjW.jpg[_/IMG][_/url]you can skip the URL part, it just makes people go to my list when they click on my signature, can fill in a site you like or youtube videos and stuff.
Make sure you load yoru picture up to imgur, photobucket, imageshack and link it in the box with the img brackets.
center brackets make sure that your signature is lined in the middle and not in the right or left.
click preview signature to see how it looks like and if it's okay, click on save signature.
this should get you going