If you're interested in signs from all over the world, including some from the UK, just check out the 3 day auction in Germany. More then 800 lots of just old advertising.
It is going to be huge. And if you just want to check out the realised prices it's also fun to watch.
You can watch the live show here. Starting on friday the 12th, 13th and 14th. But the best day is day 2, May the 13th. Some rare pieces will come up for sale.
https://www.invaluable.com/auction-house/wormser-reklame-auktion-ri6t3epby3/
Let me know what you think of it. Cataloques (3) are all online. And you will be surprised how well documented every item is. With a good discription (also in English !!!) of the state the items are in and several pictures (with close-ups)