I suspect that this is the FS-501/RPM-001 repunched mint mark variety, although there's a bit of wear on the coin that makes the secondary pick-up points difficult to make out. Maybe one of you with more experience than myself with Mercury dime
RPMs can make a more confident identification. Thanks!
Link to the relevant CONECA page: http://varietyvista.com/06%20Mercur...1SRPM001.htm