Either the top used the pen to update a "load count" that the bottom kept as hash marks on his ass, or he used the pen to mark the bottom's asshole as a fuckhole with arrows and/or a bullseye showing where to insert dick, dump load.
Loved the way the sexy, tall top dude comes in with his cock already hard. Loved seeing his ass pump up and down as he fucked. This fuck should have lasted longer so his dick lost that hardness up the bottom's butt. So the short fuck action was a disappointment because I think that top was capable of giving a stunning , long , hard FUCK.