I never did understand,how did they work?
You cut them out and stuck them in an album. This would result, obviously, in holes in your comics. This is particularly annoying when purchasing comics on eBay and the seller neglects to mention it.Anyway, here's a good site:http://www.mvstamps.com/index.htm
Ya know it must've been great cutting them out when I was a kid, now I just get bummed when I realize how I damaged my comics. The missing spots in the story pages are the worst, but I did get a discount to get into the Mighty Marvel Comic Convention.