Like many items in Plants vs. Zombies, it resembles the coins from Insaniquarium. However, this does not apply to the coins in the iOS versions, due to having different stylings.
In Plants vs. Zombies FREE, the value of this coin was changed from 10 to 1, like the other money values. However, items in the shop are decreased in price as well. This is because the game renders a values of coins as ten times more than they are internally (for example, 1,000 coins to the player is 100 coins to the game).