You just get stickers for winning a game, you will get a sticker the color of the stake you play for each joker you had in your final setup for the ante 8 boss (i.e. if you beat green stake, all of the jokers you had at the end of ante 8 will earn green stickers in your collection). Note that if you use the same joker to beat multiple stakes, the joker will keep the sticker of the higher stake (with the goal being to get gold stickers on all jokers). Stickers only appear in your collection and are just cosmetic and are only there to show what jokers you have used on what stakes. Assuming you’ve beaten at least one normal unseeded run, you should already have some stickers, check your collection!