After talking to a few of my members, here is what I found out.
The rock back in 1987 was covered with graffitti. A short time after that, the rock was cleaned off and was painted as an American Flag. Since that time, many Patriotic groups, including some of our Patriot Guard Riders, have adorned it with American symbols, to include flags. Many of the people who left things want to remain anonymous, so it is really hard to pin down one group or one individual. That’s all I was able to find out. Hope that helps you out a bit at least. Be well and if there is something else I can help you with, just email me. I’ll do what I can.