No you're totally right, it's not a pyramid scheme. I still don't think it's a Ponzi scheme though because I don't think a sticker and return postage constitutes an investment. It's just a normal, if unsustainable, trade.

For now. It would be totally consistent with how Ponzi schemes work in real life to start with something legit that turns out to not be sustainable, and then turning it into something fraudulent. Say once people have started sending in stickers they should choose to offer a service where they hang on to your stickers to save you the trouble of mailing back and forth, and doubling your holding every 10 days. Then a sticker would be an investment and it would be a Ponzi scheme.

I can only hope they'll do something like that. It'd be totally in the spirit of Ponzi.