Sock sexing

Way, way, back in an earlier incarnation, I was a Fireman.
As such, of course, we got uniform supplied. Problem came with the socks. You wear a shirt, you wash a shirt. Same for most articles. Shoes, of course were not washed.
Sox, (Now There's word to conjure with.) were a different proposition.
It didn't matter who the shirt came from there was one of it.
Came the socks, different supplier nearly every year led to a vast collection of odd black sox. Since I've now been out of the Service for O.M.G. approaching 13 years, I thought I would finally reveal the secret of keeping each pair as an entity and not having one "ankle" sock and one just-below-the-knee sock in the same pair.
Coloured thread made "sexing" them after the wash a helluva sight easier.