...even on building walls.
Even though I'm not a fan of graffiti in most cases (this one looked like chalk though, so easy to remove) I did like this example I saw recently:
What positive messages did you note during your week?
1. The ability to recover quickly from illness, change, or misfortune; buoyancy.
2. The property of a material that enables it to resume its original shape or position after being bent, stretched, or compressed; elasticity.