This is an availabitity sign you can use at an office. It can be mounted on the wall using four screws.
In order to know who is or isn't available you can insert a card (creditcard size) with his / her name on it. The slider is used to show if you are available or not.
The frontplate is clicked in the backplate and can be removed by pushing a screwdriver in the one of the holes on the backplates sides.