Graffiti on my car!

Was at the petrol station when I noticed that someone had drawn a heart and written an unrecognisable name in Japanese using yellow chalk on the back of my car's side mirror on the passenger side! Must have been some of my students playing the fool.

Got the station attendant to clean it off for me immediately...goodness knows how long I've been driving around with those chalk markings on my car!! Urghs!