if it's rented already then it's not 4rent any longer..err.. right?..
Rented.Us, a site about the % of rental homes vs owned in various US cities? hm.. this is about occupancy rather than vacancy, said the English professor.
On the other hand, "rented!" could be used to conjure up potential renters (cars, homes, appliances etc) in the same way "sold!" is used sometimes...(going once.. going twice..)