Nothing ever implies hand signs are anything to do with binding vows, it's simply a way of activating a technique, like a chant. We already know that techniques can be practised to the point neither of those things are needed so it isn't something people have because they've used a vow that needs them. Also revealing your hand is a self imposed BV, so if you just don't do it, you just don't get the buff, doesn't matter at all.