Prohibitory signs, often marked with a red circle and a diagonal bar or a red border, are placed at the point where the restriction begins. You'll encounter them frequently in urban areas, on specific road sections, near construction sites, or at border crossings to manage traffic flow and safety. For example, a 'No Entry' sign (B1) will block off one-way streets from the wrong direction, while 'No Overtaking' (B3) applies to specific stretches of road, often where visibility is poor. Signs like 'No Parking' (B6a) and 'No Stopping' (B6d) are common in busy town centres, near junctions, or on narrow roads. You'll also see signs restricting specific vehicle types (e.g., B8 'No Lorries', B9f 'No Buses') or those carrying dangerous goods (B18c). It's vital to read not only the main sign but also any supplementary plates below it, which might specify times, vehicle categories, or exceptions. Failure to comply can lead to immediate fines, points on your licence, or dangerous situations.