Now, an average person might puzzle about it briefly, shrug, and walk away.
A slightly more curious person might suppose that someone had a leaky pen and used the tissue to wipe off the excess ink.
Me: "Huh, that looks like a tissue that you use to dab up bits of blood when you've cut yourself shaving. Except that it's ink. Someone here bleeds ink. Someone here is a squidhead! An illithid walks among us!"
On second thought, I decided there was probably a more mundane possibility.
On third thought, if there is a squidhead among us, they should have at least tossed the tissue in the trash. How unsanitary. My pen could pick up diseases from that.