if youre talking about the billboards, just search for "bill" and they should come up, make sure you save them as png files and not whatever they are by default otherwise the game will just use the default textures

Thanks for your answer, but I'm talking about the Ads that goes on the bus. :)

might be worth downloading a mod from the workshop to get a rough idea

Looked through the entire texture pack and didn't see any texture that resembled those in the default ads tab.