That diamond was present on all types of RAF tactical transport aircraft at the time, but painted in various colours. On the 48 Squadron Hastings they were red. The squadron badge of course features a red Bass triangle. One morning a group of us were provided with tins of red paint and some brushes and told to go down to First Line, borrow Giraffe ladders from them, go along the parked Squadron aircraft there and proceed to extend the base of the diamonds, with the tops of the diamond extended down to it to form a triangle. The whole to be painted red. Who authorised this piece of vandalism? The Boss that's who! Thus the adornment to a rather bedraggled TG516's fin in the Squadron's Wiki entry :-
https://en.wikipedia.org/wiki/No._48...1_edited-2.jpg