I just obtained an upgraded 1917-S mercury dime for my collection. When I was swapping them out, I notice the "S" mintmark was different on the two coins. One was larger than the other, and the "tilt" was different. I went to the Heritage Coins site and looked at some photos of 1917-S mercs. Indeed, the mintmarks were not all the same. Some were larger and/or did not seem to be located in exactly the same spot. In the latest coin I received, none of the photos exactly matched it, as mine the "S" (small size) was rotated about ten degrees clockwise off the vertical. I also noted that the 1917-P and 1917-S merc dimes around roughly the same value in like condition. Neither is a key or semi-key date. So it doesn't seem like doctoring was in anyone's interest. Plus there is no evidence of doctoring when reviewed under a loop. The "S" serifs look just right. Any Merc experts out there? What do you think? Houston_Ray
Back then the mint marks were placed on the die by using a punch and striking it with a hammer. Not all the punches were identical and not everybody did it in just the same way. So it is not unusual to see differences in mint marks.
I believe the differences you are seeing are due to the fact that the mint marks were hand punched on those coins.
I don't think that's peculiar to Mercury dimes. It seems small and large size letter punches have been used on most of the coins I'm familiar with. Mintmarks are often found in various positions. Sometimes even making contact with the date, or device.
