This could be a misinterpretation of official paperwork

I was once told of an incident when the 607 squadron Demons were being camoflagued in 1936.

The official instruction referred to the underwing serials being DTD and four numbers. The DTD being the specification. The aircraft finisher on the squadron proceeded to mark out the letters DTD on the first aircraft much to the consternation of the Engineering Officer.

I could see both (-) and (/) being interpreted as a dash. I wonder if there is anything in the finishing drawings or specification that refers to a dash