There are a number of books on British Army markings. If you can, try to get the "Warpaint" series by Dick Taylor (Vols 1-4 from Mushroom Model Publications). The other "standard" if you can find it, is "British Military Markings 1939-1945" by Peter Hodges and Michael D Taylor (pub Cannon Publications December 1994)
WW2 British Army unit markings comprised 3 key elements
-Arm of service square (shows whether unit is infantry, artillery, recce, anti-tank,medical etc etc)
-Unit code (generally 2 digit number giving the role of the unit within the division, superimposed on the arm of service square)
By looking at all three elements you could determine the unit.
Generally the Divisional sign was painted on the nearside (LHS looking forward) front and rear and the unit code/arm of service square was painted on the offside (RHS looking forward) front and rear.
For airborne units, the Divisional sign would be a light blue Pegasus (winged horse) on a maroon/claret background. (Light blue and maroon/claret were the horse racing colours of General Browning) The unit code was painted in white.
I think that what you are seeing therefore is the arm of service square with the unit code superimposed upon it. Hodges and Taylor give us the unit codes for Airborne forces (specifically the 1st Airborne Division) Those ending in a 6 are
56 on a red square = 2nd Para Battalion
46 on a red/blue horizontal square = 1st and 2nd Air Landing Anti-tank Batteries, Royal Artillery
66 on a brown square was used by the 12th Devons (gliderborne air landing batallion) in the 6th Airborne Division
In his book, "World War 2 Military vehicle Markings" (Patrick Stephens Linited 1901) Terry Wise list additional numbers - included is
76 on black + second of two Field Ambulance units
46 on red/blue = Air Landing Light Regiment Royal Artillery (presumably 75mm Pack Howitzers - but note confict with information above!)
There is still much to learn and resolve
Hope this helps
Ford GPW 43097 DoD 29th June 1942 Ex M1501912/40YH40
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