In case you were wondering, those heavily armed guys are USSS counterassault team (CAT) team agents, who protect POTUS and nominees.
BTW:... This sign is considered "Legal Notice" to any would-be looters and can be used 'after the fact' as a legal defense from a Civil suit if a criminal intruder is shot on private property while attempting to loot and the perp's family tries to sue for civil damages.
I suspect as the water receds we'll see these types of "notices" again.....