Ad hoc signals have 1 dot on top of them, wifi signals have no dots. Also, although a wireless network may appear to be "open" many are not. You can connect to the signal, but you only get internet access once you login from a webpage with your (paid) username and password. This is how they do it because if you have millions of people trying to log in you need a unique way to identify them. They cannot just put a single password on their network, so they leave it open and force people to login using their unique username and password.