If you wanted to make some plaques in the style of the red and blue english heritage ones where would you start?!

I was thinking at first that I could just have custom made stickers but I don't know how long they'd survive the weather. They don't have to last a long time but a couple of months maybe.

What would be more durable? And if it was something like some plastic discs how would I write on them - I don't know what kind of company would help with this?

Anyone any ideas?