One give away early on with the no uniforms rule was luggage.
Navy had very smart pussers issue suitcase straight out of 'ello 'ello'. Air Force had very smart (joke), very large navy blue holdall. Aircrew had very smart, leather trimmed, navy blue holdall. The rules stripulated that you carried your flying kit so it was not an unusual sight on British Rail.
Anyway, about 1972, there was a rail go-slow and I was to attend a course at Scampton. Got as far as Nottingham and the trains stopped. I buggled up the SDO at Newton and a waggon picked me up in about 20 minutes. Also looking lost was a 'civvie' with said holdall. Now he could have been going to any RAF Lincolnshire base but, as it happened, he was also bound for Scampton.
Got to Newton, dropped airman off at the guardroom - see you tomorrow - and off to the mess where I was met by the staish.
He apologised that he could not let MT run me to Scampton but had got Scampton MT to pick us both up 0830 AM.
Now without the visual clue he was an airman that man would have been in
sh1t one way or the other. Either sleeping rough, hitching, dossing, late or out of pocket.
Mind you, if you know, there are still signs. At Heathrow I saw four men collecting 'tickets on departure' which is one sign. Their appearance was another. They were almost identikit alike and I am 100% certain they were army and at least 50% sure what regiment.