UK roads signs
 

Since we decided to rent a car, my hubby found this site and started reviewing this site everyday for about a month before we actually left for England.

They even have a mock test you can take to see how you are learning.

Here is a link to the site:

UK Road Signs - Road Signs Giving Warning

We didn't learn all of the signs, but we knew most of them and didn't have any problems.
This is very helpful to anyone who is considering renting a car in the UK.