There are two mint marks for San Francisco in 1942. Your’s appears to be a normal MMS-005. http://varietyvista.com/06 Mercury Dime/San Francisco Mintmark Styles.htm
These are tough especially on a worn coin. Look at the top serif on yours, the straight line serif is on top and it’s on the bottom on Wexlers. Like I said, the wear makes it hard to differentiate the serifs. It’s still a good coin!