I have had the good fortune to work with the Estate of Andre Kertesz. This has been a real eye opener regarding the world of of collectible photographs. My opinion now is, pencil if possible, and the more info on the back the more the collectors like it. As far as signing on the front, I don't -- I feel like Dave Martini, above, that it can be a distraction. I once had a painting teacher say, "Think of the signature as still another color, and consider it carefully.
Regarding mounting on board, it is strongly frowned upon in most instances. As artists, though, we have the final say, and it may not always be creatively satisfying to follow the dictates of commerce and convention.