Why would a thief need to highlight it? Are their memories that bad? They'd have to remember where the van was regularly parked up, and if they can remember where to go to find the van then its going to be pretty obvious to even the most forgetful thief that the 2 tonne box on wheels is what theyre looking for.
Sorry, I was a sergeant on an autocrime team for 7 years and heard it all.
But coming back to the mark, you reckon it seem like a spot with no paint that goes right down to the bare metal?