I forget the exact number, but each Commando did have a handful of Carriers on strength. Found in the Support Troop, if memory serves?
For 1 Special Service Brigade, the Arm-of-Service marking was a red square with '81' in white. For 4 Special Service Brigade, the marking was a red-over-black square with '100' in white. They don't appear to have used different numbers for different Commandos.
I'm not sure if they used a formation sign - the Armoured Support Regiments didn't, but it was probably the circular combined services badge - red on dark blue.