Most likely they would ask if you have permission from the owner of the property.
Real graff writers have a Portfillio of pieces and artwork that they carry around to random stores and businesses in hopes that the owner will let them paint on the building. I did this at a minimart last year and the police did actually stop and hassle us. We showed them the note thing that the store owner gave us as permission and the cops were cool about it and just left. About a month ago there was a sick, perfectly smooth wall that was part of a shipping warehouse, but it was in a really high traffic area. We ended up making dummy papers to show to the po-po in case they ever dropped by but we never had to use them...
Is your location in a high traffic area like a roadway or sidewalk?