My Dad was in the merchant navy in WW11. Unless you were officer class, you didn't have a uniform. He was on leave on one occasion and out with his FiL for a drink. He wasn't officer class so no uniform. He was turned on by one individual as being a coward - "what's a young man like you not doing his bit for the war?" (I'm wording this minus the swear words).
Dad pointed to his small badge on his lapel - "What's this then, bl...y scotch mist?" It was his M N badge. That's all they had to show they were serving. It wasn't very big, so easy to miss.
He did the Russia run on many occasions, plus the Med and Egypt. Most certainly not a coward. How quick people are to reach conclusions, though. In truth, like many others, he went through hell, but do you know, like many, he hardly ever spoke if it.
He didn't relate the above story about him being accused of cowardice, by the way, his FiL did, who had been in WW1.