We had a request from someone to stop AirPort Express broadcasting the SSID, for security purpose.
Hiding Wireless network SSID does not really enhance security.
Unfortunately, this tactic may lead to a false sense of security, as it only impedes casual wireless snooping, and does not stop a determined attack on the network.
There are numerous of tools that can scan any hidden SSID.
Just in case anyone still want to hide their AirPort Express or AirPort Extreme SSID:
In AirPort Utility, go to “Wireless” and click on “Wireless Options…”
Check the box for “Create hidden network”