Those look like the standard tact board markings used in armor battalions but painted on the side of the vehicle.
The outside square represented the battalion within the division. The geometric symbol could be a square, circle, hexagon, heptagon, pentagon, octagon, etc.
No tan or yellow symbol inside was a battalion HQ vehicle. The geometric symbol inside designated the company, square=A, circle=B, triangle=C, diamond=D. (or so I think).
The Roman numeral inside was the platoon, I, II, III.