Doesn't seem too difficult, just have it popup a page which shows the line of the users profile which shows the signature on a new page (possibly a popup).
I'm not too sure how to go about the "Preview" part though, you'd have to come up with a way to set a file with the information, even temporarily so that the popup could contain the signature information...
Well, now to sit back and listen to people yell at the Gizzy ::sits::...
