I've never liked "For Sale" or "For Rent" sky art displayed on the World Map. I think it's an ugly, cheap-looking eyesore and stupidly hides the actual land beneath it from actual view of potential customers on the World Map, which seems like a counter-productive thing for land owners to do.
The World Map already has a "Land For Sale" filter built into the World Map, so there's no actual need for "For Sale" sky art signs to be rezzed inworld like they are. So "For Sale" sky art should be discouraged and stopped.
However, no such "For Rent" filter currently exists in the World Map. I think it's time for a "Land For Rent" filter to be added to to the World Map.  Rental payment boxes owned by CasperVend (which is owned by Linden Lab now) rezzed into rentable parcels could potentially be linked into the World Map filter options.
Land owners who wish to advertise their land for rent, but who chose not to use CasperVend payment boxes, could benefit from a new Land Settings option which then displays their land as "Land For Rent" in the proposed World Map filter option.