They are known as signatures and you need to keep your pictures at a maximum of 500x250 as they can cause problems otherwise.
Upload your pic to here imageshack.us/ and copy the url, then click on your user name on the left or profile at the top of the page and go into modify profile (you may have to put in your RK password again to modify)...look for the part which say's signature then paste the url for your pic into it.
On either side of the url you have to put your url in the middle then [/img*]....but not with the * I put that there to stop it working in this post.
You do the same with the avatar pic you choose under your user name name, you copy and paste the url into where it say's avatar, but you don't have to put the tags in there (ie )
I didn't make the one I've got.....I have no idea how to. I asked on EastendersOnline if anyone could make one for me, and that's the one they made and I quite like it actually.....your best bet would be to ask on EEOnline......Sorry!
in eeonline, you can ask a girl called hannah_s in the creation section of the forum. she i feel is the best ee signature maker , i know, i'm an admin there lol, well co-admin