note painted gauges
I painted a Randy Carter(RC) gauge just below the Rt. 340 bridge on Gooney Run(VA) back in 1988-89 using a cheap can of automotive primer gray spray paint I had in the garage. I made a cardboard template using lines at 1/2'(a short line) and 1'(a longer line) increments.
It's still highly visible to this day. No prep. Just paint.
The gauge I had spray painted at the putin was done the same way. When bridge was replaced a buddy painted another on the new head wall using a forest green color and some fancy arrows. Lol...