Why Is This Sticker On My Trash Can?

When I got home from work a few weeks ago, I noticed that my roommate had put the trash can back near the house (it was garbage day, and it had been at the street for pick-up).

When I turned into the drive, my headlights illuminated something on the can that caught my attention, so on the way into the house, I looked at the can more closely and noticed this sticker.

My thought is that I put something into the can that I wasn't supposed to have in there. My second thought was that my house was being marked for some reason. My third thought was "aliens!". (I quickly disregarded that thought, shortly  after an abduction scenario ran through my head.  I enjoy the scenarios all the way up to the probe part.)

So, if this is a mark on my house/can, what is its purpose? Is it marked for replacement? Repair (not that there is anything wrong with the can, I take pretty good care of the thing)?

What do you mean "you should call the waste collection people, they could tell you"? If I call them, they'll know that I am on to them!