Thanks for this anon! Well, let’s see bcz I have definite thoughts about this…
Thomas doesn’t really have any distinguishing physical marks that we know of, BUT James likes the way the lines at the corners of his eyes get extra crinkly when he smiles and the bigger he smiles the more crinkly they get.
He gives a lop-sided grin every time Thomas raises his finger to cover his lips when he smiles as if to hide it, but he’s looking directly at James when he does so and James thinks it’s hot.
James definitely likes Thomas’s hands, specifically his long fingers. He’s always though of them as elegant but after they become lovers he discovers other, more intimate reasons to love Thomas’s fingers.
And an idea I’ve used a couple of times in fanfic is that Thomas has a reddish little birthmark on the inside of his thigh. James likes to kiss it when they’re just being lazy in bed together because he loves that he’s the only other living person who knows about it.
And post finale, I like to think that James likes his beard too (I love both of them with beards), but Thomas does shave it for the first time after their reunion in the summertime so James can look and feel the smooth face he first laid eyes upon all those years ago. And James can’t stop touching Thomas’s chin and jaw and it makes him emotional. He loves Thomas’s face but he also likes it when Thomas grows his beard back out again in the winter because, you know, bristles against places. ❤