In Arcola Ill. one of the murals ( Lawn Rangers ) had a small picture of Obama holding a broom leading the parade he did this once & they wanted it on there, a local artist painted it & did a awesome job.
It was clear coated soon after because knowing full well it would be tagged, it was, then cleaned off no problems.
But I do believe it was a 2 part automotive clear coat ... Bill Diaz had the right stuff ... I looked for it but no find.
Although Ronan's Aquathane & Modern Masters clear coat are what I use & can remove paint off them ..not over & over.