The tanks in Fred's photos all have a set of markings painted on the front and back. As an example, here's the front of the Comet tank at the Museum of Coastal Defence:
I wondered what they all meant, and turned to Steve Pannell for help. Steve is researching the Comet tanks that were based in Hong Kong. Steve then asked Dick Taylor, and together they provided a very good explanation. Here's the summary:
Left square: The number ('2' in this example) represents the Arm of Service number, a type of code. The background colour(s) tell you the type of unit; red over yellow for RAC (Royal Armoured Corps). The number, combined with the Formation badge, then identifies the actual unit.
The example above means this vehicle belonged to the Corps RAC regiment. Some of Fred's photos show a '41' instead of '2'. In 1950, '41' on a 'red over yellow' square meant it was part of the RAC regiment in an Infantry Division.
Central Vehicle Registration Number: This is a number that uniquely identifies a single vehicle. Orignally Comets were given 'T' numbers (e.g. T335335). But since 1949, the British Army has used a '2 number - 2 letter - 2 number' format for vehicle registration numbers. The middle letters 'ZR' were assigned to any vehicle that was built before the 1949 census. All the Comets in Fred's photos show ZR, for example.
The MAFVA website gives more information about the registration numbers. eg they show the list of registration numbers for Comet tanks covers the range from 09ZR21 to 21ZR52. No other type of vehicle should have a number from within that range.
Most of the Centurion tanks in Fred's photos also show ZR, so were built pre-1949. However at least one was newer - this photo is a bit fuzzy, but the registration number is visible as 09BA35. The MAFVA document dates this to 1950-51.
By now you may have spotted that the number on the museum's Comet is completely fictitious. I suspect it was put on there by the Quartermaster who was responsible for the barracks it was in (hence the choice of QM), and the numbers represent 1948 - 1984. The name on it (Nina) is probably his wife or daughter.
Right square: The emblem represents the main 'formation', in this case the Gurkha Infantry Brigade. I've a feeling it was actually the 48th Gurkha Infantry Brigade, to which 1st Royal Tank Regiment would have been attached at the time, so that is probably where this number has originated.
Other markings: Troop numbers appear inside or alongside the squadron markings on the turret - triangle for A Sqn, square for B, circle for C, and diamond for HQ.
More about the museum's tank: This is the only Comet remaining in Hong Kong and was kept originally as a Gate Guard. The markings have changed over the years as it has been repainted and they have 'drifted' in accuracy.
The Hong Kong Coastal Museum Comet has been restored quite well, but the main gun barrel is suspect and they have added a second machine gun to the turret where the gunners sights should be!