Bleach

I have these Bleach pens that we used to use to make tshirts. I thought, hey, why not use them to write on everything. So, here's me testing it. It's a little tricky, cuz it's drippy. But once you get the hang out it, it's quite nice.
Downside is that you have to return to capture a picture, because the bleach takes 15+ minutes of work, and I don't know about you, but I'm not going to be hanging around with a camera, waiting for my graffiti to appear.

Other places I tried were brick and bathroom stalls. Tomorrow I'll see how those did.