Sorry if this is a naive question, but I just bought a black off-the-peg suit jacket that has a loosely stitched blue thread across the top of the shoulders. I've seen this sort of thing before on more expensive jackets, but it's never been on one I've bought before. So what is it and what's it for? I assume I'm supposed to cut it off, as it's the same blue thread that's been used to loosely stitch the side vents shut. I've attached a photo.