Hard to say really; a signed print from someone famous is more valuable than an unsigned print.
Side story thats sort of associated. I took pics of the Space Shuttle Enterprise flyover the Hudson River recently. I printed out some shots to show the staff at the Treatment Center I was going to and gave them to the receptionist being that she has three young sons. They loved them, but then asked her why I didnt sign them. I was puzzled stating that Im not famous or anything, but she said they like to have them signed by the person who created them. I told her no problem, just bring them in and Ill sign them. Go figure!!!