What the hell is this mess? I'm really trying to verse myself in coins but then this happens! Sideways mint mark? Corroded? I'm annoyed.
Why are you annoyed? It looks like something @paddyman98 sweeps to the side on the sidewalk. You better use rubber gloves! It looks like something that would come off with warm water or acetone. I think it's just gunk on your coin.
Clean it with warm water or acetone and you should see the mint mark if there is one. I'm not ever sure if that's where the mint mark is located.
It’s just a rot blister. To small for a mint mark. http://varietyvista.com/01b LC Doubled Dies Vol 2/Denver Mintmark Styles.htm
Judging by all the green stuff on it, that's some serious environmental damage. Chuck it in the leave a penny tray.