Anthem doesn't always have to be national, some leagues/ cups have a tune or "anthem" that plays when the players walk out, re: Champions League. Name probably came just based off of international play as you and Christopher Jee presumed and made its way to domestic leagues. With the anthem jacket wearing, you do only see those worn when the players walk out. Haven't seen them used for bus/plane trips or practice when it's cold. I could be wrong, but that's my quick opinion based off of what I've seen.That was a guess I had as well, and came to the same "too easy" conclusion. We also have travel jackets and warm-up jackets, and do teams really switch into these just for the anthem? Further, non-US clubs have them, call them anthem jackets, and most sports leagues outside the US do not play their national anthem before sporting events. It also seems to be just a soccer thing.