I'm sure it's bindun, but...
I have a habit of, when redecorating, leaving little messages for the next people to uncover.

Under a new lounge carpet, on a rectangular section on the concrete that I especially discoloured: "the bodies are under here"

On some plywood I used to cover up a boiler exhaust (before I put the wallpaper up): "have you found the bodies yet?"

On the underside of the floor on a new shed: "If you are reading this, I was killed and buried here. Please tell the police!"

Under the sand I used to level the ground, before I put a new brick patio down, I put a grotesquely twisted white tape body outline - with a severed head - and some scraps of "police line, do not cross" yellow tape

Under the wallpaper, on a fairly thick wall on an old house in Somerset "Have you found the money yet?"

On some breeze block I used to block up an old central heating vent: "IRA Arms cache - do not open"

I've been the recipient or witness of a couple, too:

Once, I was *ahem* fixing the odometer on an old Cortina. I opened it up and there was a little note inside: "Oh, no - not again!"

And - a pearoast - a mate's BMW kept getting broken into, and the radio nicked, while parked in a multi-story car park in Bristol. Eventually, he got sick of it and didn't bother with a replacement. He left a note on the dash saying "no radio fitted". Someone smashed the window and wrote on his note "just checking"
(lustfish, Sat 16 Jan 2010, 5:27, Reply)