Tim,
I believe Varsities of the RAF Signals Command based at Watton,Tangmere and Cottesmore carried the orange/black cheatline with the nose zig zag flash. Some of these aircraft found their way into training units hence the mix. The CAW machines carried the blue thin cheatline with aircraft numbers on the nose and fin,whereas other units used alphabet letters.
The machine in the photo at Singapore was probably loaned to the CFS and being used by "trappers" to check out Valetta crews ?