I thought that a Ponzi scheme was simply one where returns to existing investors are paid from the capital contributed by new investors.
If you give the returns immediately (the two stickers) with no option to reinvest, the ponzi scheme is going to run out of steam very quickly and there's no way this is going to attract a lot of people.
In summary, this is a Ponzi Scheme, but not one that has a lot of chance of being sustained for very long.
A Ponzi scheme is centralized, with new participants joining directly with the scheme, and proceeds paid out to all existing participants.
As structured, this sticker scheme is a Ponzi scheme, since it's all centralized and you don't do anything besides send in your sticker and postage.
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.
But it's definitely meant to mirror the structure of one, just with stickers instead of money. If they had you send in $10,000 instead of a sticker, and promised $20,000 back, it would clearly qualify.
So I'd say it's "a Ponzi scheme, but for stickers."