Circa 1810-ish.

Okay, what I should like to be able to do is to have an army officer, someone who has seen action in the the peninsular campaign, come to the rescue of another guy, who had also been in Spain. My second guy had not fared so well and had been invalided out of the army. His injuries are not obvious unless he takes his shirt off.

What I should like, though I do not know whether it is plausible, is for my Samaritan officer to know without having to be told that the other man had served and seen active service. One hears stuff about the way a person carries themself, the way they move, maybe a hyper vigilance, but I don't know if that is a load of over blown tosh, or there is real mileage in it.

Might there be some sort of insignia/badge my injured guy might wear on his coat?

When I say officer, I mean commissioned officers, though my injured guy is a former lieutenant and my Samaritan is a colonel.

I doubt it's relevant, but they make each other's acquaintance in a drawing room in a fancy house.