According to the documentation for the D620
The Bluetooth icon:
Turns on when Bluetooth® wireless technology is enabled. To enable or disable Bluetooth wireless technology, move the wireless switch to the "on" position. See wireless switch for more information.
NOTE: Bluetooth wireless technology is an optional feature on your computer, so the Bluetooth icon turns on only if you ordered Bluetooth wireless technology with your computer. For more information, see the documentation that came with your Bluetooth wireless technology.
So there should be additional documentation for the Bluetooth option, if present.