Remember when you would open up a wax pack and there would either be a piece of gum stuck to a card or gum residue caked on the card's surface?
Well, there must have been a case of gum next to this card. It's a mess!
If I didn't know any better, I would wonder if it were mold growing on the card. But since I've had the card a while now and it hasn't grown any fuzz, I think it's old gum residue.
Come to think of it – it could be orange juice. Maybe it's the dripping of an ice cream or the remnants of a Snickers bar.