Mac OS X 10.6: Using the AirPort status menu to control AirPort
You can display the status of your AirPort connection in the menu bar. You can use the AirPort status menu to switch between AirPort networks, turn your AirPort Card on or off, open Network preferences, or create a computer-to-computer network.
To display AirPort status in the menu bar:
Choose Apple menu > System Preferences, and then click AirPort in the list.
If AirPort isn’t in the list, click Add (+) at the bottom of the list, choose AirPort from the Interface pop-up menu, give the AirPort service a name, and then click Create.
Select the “Show AirPort status in menu bar” checkbox.
Four signal bars appear in the AirPort status icon in the menu bar. The more bars that are black, the higher the signal quality.