Do not believe it is illegal to run ads on property that you have not closed on. I would wait until I had it under contract before trying to sell or advertise.
I have seen a lot of addresses posted on the side of the road for Open Houses, Garage Sales. regular house for sale signs and the like. If on the ROW they are illegal. I believe the city just removes them and that is about that. I see a lot of builders etc putting them up on Fri PM and taking them back up on Sun PM. This may be a good idea for you too. They are the expensive metal ones normally. May be good to get permission from property owner and place out of ROW just to keep them up longer too. Just some thoughts I had on the subject.
Happy Holidays and Thank you,
Ted P. Stokely Jr
11505 Sw Oaks
Austin, Texas 78737
512-301-9171 home
512-587-6177 mobile