Definitely all aircrew trades, Danny. I've seen photos of several eventual gunners with the white flash too.
There's a great collection of oral history transcripts in the
Australians at War Film Archive, which I've had cause from time to time to peruse. Here's an extract from the interview of Lionel Rackley, who would eventually become a 630 Squadron pilot - which this discussion reminded me of [my bolding]:
Originally Posted by Lionel Rackley
See, air crew trainees went into a place and they were there for a month, six weeks, and went out again. But the ground staff people were there, so the town belonged to them, really. In those days, we used to wear a forage cap, and air crew trainees wore a little white flash on the front of the forage cap, that denoted us as air crew trainees. And these ground staff, they had set word around Temora that out at the aerodrome there, there's a venereal hospital. And all those fellows around town with white flashes on their caps, they're the patients. So we had to live with that, in Temora. And I've spoken to other fellows and ground staff did that in other places as well. They did strange things to air crew trainees.
Those sneaky ground staff!
Adam