It is my understanding that these pennies are made for the
Mark Masons, who use them in their rituals. At one point, a Mark Mason is expected to invent a "mark" or symbol for themselves and then take one of these pennies and engrave their "mark" on the blank circular space in the centre of the keystone. That penny then functions as that person's ID badge within the Order.
That is why these pennies can come in two varieties, "marked" and "unmarked".
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis