I don’t know if there are formal rules around the use of these flags (I assume not), but, fwiw, as a trans person myself, I like seeing them worn in general. I don’t really assume or care too much about the person wearing them, but I find it reassuring. Both in the sense of, “hey, at least this one person probably doesn’t have a problem with me existing. One less rando for me to worry about”, and in the sense of, “hey, at least this one person can openly exhibit a symbol of trans support and visibility without having been crucified for it. Hopefully that means I’m unlikely to catch flak for not passing around these here parts”.