look at this guy's signature
http://forum.toribash.com/member.php?u=479759
how can he write [Ka] With the link at that words?
please help me

It would help if you could reword that, since I don't understand what exactly you mean, but if I think I know what you meant, are you asking about the link? It's just an inserted hyperlink.

You just copy a link, select text on your post/signature, and click Insert Link (next to the A with the black bar underneath).

Then again, you have the same one in your sig, so I'm confused.