A good question. We will assume that for purposes of erase 'writing' includes sigil, marks, designs, and symbols (though not the symbol spells). By RAW, the erase spell specifically says the target is one scroll or two pages. Reading the spell description, we see that it specifies removing magical or mundane writing from a page, parchment of 'similar surfaces'. Whether you consider a wall to be a similar surface to a paper or parchment, or whether you consider flesh to be similar will determine your decision on removing writing from those surfaces. So, by RAW, the spell technically doesn't.
However, if we look up tattoos, specifically under Inscribe Magical Tattoo, we see that an erase spell can permanently destroy a magical tattoo. I don't see why being magic would make a tattoo more inclined to be erased than a non-magical one.
So while RAW might not state or seem to support it, reading further on interactions with magical tattoos and erase would seem to highly imply that flesh is similar enough to vellum, which is similar enough to parchment that it is a 'similar surface'. Or that erase just does work on them, if you don't want to play the connect-the-dots game.
