There does seem to be an S, but hard to tell what's crud and what's metal. I believe they used the "tall" mintmark in 1954: http://varietyvista.com/San Francisco Mintmark Styles.htm Kinda looks like the pointy top serif appears on the surface of the D. If it is an actual D over S that would be an awesome find.
I think it is very interesting. If I owned it I'd consider sending it to an attributor for an opinion.
Yes there is! Soak it in pure acetone. Not nail polish remover, pure acetone. You can get a nice jug at Walmart for around $7.
I think the genuine D/S varieties are more pronounced. The one I have slabbed has a decent part of the S hanging out of the bottom of the D.
The only over mintmarks (OMM) I know of for Jeffersons are shown here on Mr Wexler's page: http://doubleddie.com/939955.html There is a Cherrypickers variety RPM-003, but it does not look like your coin.