1968 Quarter Mint Mark Double Die Error?

Hi! I'm new here on Coin Community but I have been collecting coins of various value...(Wheat Pennies are my favorite but still collect any numerical value) for sometime now and have come across this 1968 Washington quarter with an intriguing possible mint mark error. It doesn't look like PMD(Post Mint Damage) due to the fact that the mint mark is raised considerably, and tou can see there is a "D" but more like a double die error either D/D or D/S. In certain lighting it looks like you can see a "DS" and in other lighting looks like a "DD". Also thought could be a Cud error with the mint mark. Any feed back or general info that anyone knows about this would be greatly appreciated! Thanks~Dayle J.