Road sign graffiti

Why?  I'm pretty sure there's a fine for painting on road signs but highly unlikely that the culprit would ever be caught. No idea what motivates anyone to do this.
To town today to drop off recycling, fill up with gas and pick up some groceries. I'm regretting that I didn't get in a walk because the weather was decent, heavy frost this morning, some rain, but mostly sunny. Rain expected for the next few days. Good thing I'm not a fair-weather walker!