'Give way', 'Yield', 'You do not have priority'!

I wonder whether British Motorways need to have a sign such as 'Give way', 'Yield', or 'You do not have priority', when getting on to a motorway. Slip roads are not the best places to judge the speed and density of traffic when joining a motorway. Caravaners in particular cannot move over to the middle lane easily if there is already a continuous flow of traffic there. It might be worth having a reminder to vehicles entering the motorway system that they need to be just a little bit more cautious on some of our congested motorways. Am I being unreasonable? What do you think?