Cleaning a caboose

I was called about cleaning the red caboose on the riverfront in Knoxville TN. The streaks were not coming off with the usual methods, so I had to experiment. I wondered if the streaks were concrete dust from the rebuilding of the Henley Street bridge. What ended up working was a fine 800 grit sandpaper with an adhesive backing on a 6 inch dual action sander.
When I started working, the “Vol Navy” was there, and later, a large millipede (?) was walking across the sidewalk.