What the see outlining the mintmark is part of the letter punch stock. It normally is not transferred to the die unless the punch tool is given too hard a blow. This is common among gold $ and $2.50, and other small coins, although it is seen on double eagles through 1904 on the IGWT logotype punch.
This description from numismatist Tom Delorey should help.
Making a single letter or number punch is a skilled bit of engraving that can be accomplished one of two ways. The engraver can take an annealed (heated to soften it and allowed to cool slowly) steel rod and, using small punches and files, cut away the metal at the tip of the rod that is not a part of the character he wants. Think of a raised letter on a tombstone that is created by removing the unwanted stone in and around the character. After smoothing and finishing the surface, the engraved punch can then be hardened by heating it again and quenching it suddenly in a bath of water or oil.
The second way is to take a block of heat-softened steel and carve out metal in the shape of the desired character, working in mirror image. The same process was used in the early days of the Mint to create large designs such as a Liberty head or an eagle before reusable design hubs were created, so carving out a small letter or number was not a great challenge to a skilled engraver. When finished, the block could be hardened and the end of a softened rod hammered into the carved recess, raising up a positive image of the character. The raised image could then be touched up and smoothed out before the rod was hardened.