At the time the army was transitioning from the Second World War system with squares to denote the unit and other signs to denote the vehicle's subunit and role. For example the armoured regiment used a red and yellow square bisected diagonally with the number 2 painted on it. For individual vehicles they used the same system as today. The artillery, on the other hand, used a red over blue square with 13 painted on it. For individual gunner vehicles there was a system of red squares taking up one quarter of the blue square, starting for the senior battery in the upper right corner and working clockwise to lower right, lower left and upper left. Instead of the casll sign a combination of letters were used. For example Z was the CO, X for each of the battery commanders and guns were based on the troop letter and A to D, thus C Troop guns and gun tractors were CA, CB, CC and CD.
We were moving to a system that used the NATO tactical symbols such as you would find on a map along with the call sign, much like what was in use when I retired.