On macOS Sierra, if I go to System Preferences > Bluetooth, and uncheck "Show Bluetooth in menu bar", the symbol remains stubbornly visible.
How can I make it invisible?
Usually, rebooting the system fixes it.
Try holding down the Command key and using the mouse to drag the Bluetooth symbol off the menu bar. Alternately there is a check mark to uncheck in the bluetooth preferences in System Preferences.
You may also try to relaunch the Finder. Hold 'Alt/Option' key and right-click Finder icon in the Dock. Then select Relaunch command.