Although The Highway Code shows many of the signs currently in use around the United Kingdom, a comprehensive explanation of the UK’s Road Signage System is available in the Department for Transport’s book, Know Your Traffic Signs, which, you can download for free at the bottom of this page (usually £4.99 in bookshops).

Note: Know Your Traffic Signs is quite a large PDF download – around 5MB. You’re best downloading this on a WiFi connection.