You can just make out the AoS sign on the back of the trailer here, which would suggest that AoS signs and formation signs were carried:
I've also found one (again 141 RAC) with a squadron sign clearly visible on the turret rear ('B' Sqn square with troop number inside), but can't link to it.
However, as always, it's often extremely difficult to tell, as the photos are in black and white, meaning that it's often extremely dificult to spot different colours, added to the fact that they're often plastered in a layer of crud and/or camouflage/stowage/track-links.
As Derek says, I would be extremely wary of using museum pieces or gate guardians as a guide, as even Bovington has some howlers in that regard.
Re seniority – 141st RAC remained the junior regiment in 31st Tank Brigade throughout the war, so the only change was the change in formation sign. 7th RTR moved from senior to second regiment, so also changed its AoS sign.