@chrisblue77: Why would you when you start? Finish it first and if it's worth keeping it, sign it and date it. That way you create a history of where your breakthroughs in improvement where over the years.
Really? Im just passing tips handed down from professionals working in Marvel and DC that I know on a personal level. These tips have served me well for many years. It comes down to personal preference but its not good when you look back and dont have dates. I know because I have a few pieces that don' t and its hard to pinpoint the time period they where drawn. To each his own.
I don't sign sketches. If it isn't a finished work, it's not worth signing in my opinion. If you like to keep your stuff labeled, you can write some info on the back or something. Or if you use BlueLine comic pages there is a place to label these kinds of things if you so choose. But for the work I do I only sign it at the end.