Ok, Katon first of all this is like totally in the wrong place....So I am going to move it over to the Help section of the forum then pick back up. ^_^
Ok as far as I know, you can't direct link a pic from a Url... To get a pic on your sig you need to save it to your comp and then host it at a site like photobucket.com or imageshack.us
Once it is on there, the site will give you a bb code some that starts with
this is code you need. Copy it and paste it in the SIG part of your profile.
If you are still having troulbe and want to test all this....there is a test your html code section, here under help... that's what its for... type in your codes and see if they work.
Hope this helps if you have any more questions, please post them here in this section!