More to read on:
https://northeastnews.net/pages/remember-this-trading-stamps/

" Commonly called “trading stamps,” merchants across America offered savings stamps based on the amount of the customer’s purchase. The more one purchased, the more stamps were obtained for the cash transaction.

Stamps were pasted into savings books and when full, could be redeemed at a redemption center chock-full of name brand items, from household goods to appliances, home decor and toys. Depending on the merchant, the stamps offered could be Gold Bond, S&H Green Stamps, or Top Value, among others. "

I think, it work like royalty promotion, isn't it ? Can someone enlightening me on this stuff.

Perhaps it is not like food/fuel/clothes stamps in the Soviet ?!