The windscreen is used to protect the occupants of the vehicle from the elements, but in doing so it must remain clean and clear for maximum visibility.
However, we are required to place certain things on display on the windscreen, whilst many other things are prohibited.
You are not permitted to stick anything unauthorised in the windscreen, so things like ‘For Sale’ signs are forbidden. You can place a GPS or mobile phone cradle or dashcam in the windscreen, but it must not interfere with your primary field of vision.

Here is a list of things which are permitted. When we talk about the location of them, we are imagining ourselves sat in the vehicle, looking out.

ITV Sticker (if required)
The ITV sticker should be placed in the upper right corner of the windscreen (remember we are sat inside and looking out when we describe the location). Also, you must only display the currently valid sticker, not a collection. Only one sticker should ever be displayed.

ECO Sticker
Although the Eco Sticker is not mandatory, there are an increasing number of cities where restrictions are in place for vehicles which are not displaying the sticker, or for vehicles who do not satisfy a minimum standard of eco-friendliness. If you drive into one of these areas without the appropriate sticker then you face a fine.
You can obtain an Eco Sticker from the main post offices in exchange for a small fee. Remember to take the vehicle´s logbook with you.

The Eco Sticker is to be placed in the bottom right corner, again, as we look out from within the vehicle.

Shared Vehicle Sticker
Some towns and cities offer special lanes for vehicles where the occupants ‘car share’ in order to reduce the number of polluting vehicles in some areas.
Special lanes for these vehicles are advertised as being for vehicles of high occupancy, VAO.
The shared vehicle sticker is placed in the upper left of the windscreen.