Thanks very much Greg Mac, that seems logical.
So where might the C coy engineers have been stationed?
And Tommy, that pic explains the bars. If you fill in the faded bits - it could be 'DP'
Only the curved bits are faded the straights look like tape?
I measured 1" wide on mine before sanding and they just got fainter, so they may have just been tape residue painted over.
Seems there are no other door markings on that FFR.
Do you know where the pic was taken?...looks like an exercise round about lunch time!
Many thanks again for your input.
Rob.