Hello Erik,
At the time of this aircraft being interned, 60 sqn markings consisted of a white circle behind the cockade on the fuselage and repeated above behind the headrest.
The individual aircraft letter or number appears to have been painted in front of the cockade and repeated in enlarged form on the upper wing centre section. It may also have appeared beneath one of the lower wings in black or even cockade blue.
As this was from a batch of 200 constructed by the Royal Aircraft Factory, Farnborough, it would almost certainly have worn the wing cockades in the inboard position, just missing the ailerons. The serial would have appeared on the fin in white.
I don't know the allocated letter or number of this particular aircraft, so I've shown it as 'E' - it would not have been 'A', 'G' or 'Z' as these were usually reserved for the flight commanders (or '1' if numbers were used for 'B' Flight).
As the Dutch cockades have been painted in the outboard positions, the British ones (if they were in the inboard position) would have been painted out (peresumably in a light colour beneath the wings). The letter on the upper c/s would also have been painted out.
Here's my best guess at a before and after side view:
I've missed off the LVA letering and serial number!
Incidentally, the SE5 file lists this aircraft as having a 150hp Hispano Suiza engine when built, but the LVA designation indicates that this was replaced at some point with a 200hp version.
Hope that helps!
Edit: I've just noticed that you mentioned that the aircraft was from 'B' flight, so it would therefore have been marked H,I,J,K ,L or 2,3,4,or 5 - not E as I've shown it.