Wouldn't a dog whistle be a type of shibboleth?

Dog whistles convey a message to those in the know, but without outsiders being able to hear it. (Like how a dog can hear a dog whistle but humans can't.) A shibboleth would convey that you're a part of an identity group without outsiders being able yo tell the difference.

Though I suppose dog whistles could also be phrases instead of words. Idk, there's at least some overlap.