All U.S. states have laws prohibiting electioneering near polling places. "Electioneering" is the act of attempting to persuade someone to vote for or against a particular candidate. Each state has its own laws, but all 50 states prohibit electioneering inside of polling places and within a certain distance outside of polling places during voting hours. Ohio election law, for instance, requires that "two or more small flags of the United States...be placed at a distance of one hundred feet from the polling place" to designate the electioneering boundary.
Certain states also include "passive electioneering" prohibitions at polling places against apparel and paraphernalia that convey support or opposition of a candidate.