I see “advertising”. I did a Google search and there is actually a company called advehicles, so it has some potential.
Quite a few things working against you:
- advehicles(.)com is for sale, and you need to know what they offer and set a price below that
- advehicles(.)uk and advehicle(.)uk are available
- There are companies called adCars, so potential buyers might choose alternative
“vehicle” can mean “means”, so “advehicle” can be either about cars or advertising in general. When you have a plural form, you are restricting your market use.