GoldLeader

Yeah. I mean I don't remember this one specifically, but I remember a lot of US companies used to do a cut out the barcode type thing where that proof was sent in and you got either discount on a new game or a free game.

They did it in the UK but only on budget games and only with very few titles as well... 

I bloody hate having magazines with discount coupons cut out ! I never cut anything out of mags but some people were almost pros at it!

Parker Games had a proof of purchase  printed on the inside of the front of the manual.  Often see the bottom right corner cut out in listings.

That's better, though, the manual. When it's the box or sleeve that might have been too much for me.

I know I love free games (I grab my fair share over at |GOG.COM), but I don't know if defacing a game I had already paid for would be something I would do.

In my case, I had hundreds of games, but usually it was later, than everyone else, when I could afford to buy them.

By the time I got to them, any promotional offers - invariably had expired.