If you look in your guidelines there is a clause that states that the gas station signage (I almost put the name... ooops) has to be present at HALF of the available spots.
So if there are 8 spots available for advertising... there should be AT LEAST 4 of them that have the gas station current signage.
You do need the guidelines though because it is slightly different for different stations.
Good Luck!!
O.o o.O
Happily shopping New England and beyond!!!!!