I think its called "electioneering". No political banners, signs, what not within so many feet (100, 400 or something, I forget) of the poling place.
The poling place is supposed to be a "neutral" area.
California law:
- ELECTIONS CODE SECTION 18370-18371
18370. No person, on election day, or at any time that a voter may
be casting a ballot, shall, within 100 feet of a polling place or an
elections official's office:
(a) Circulate an initiative, referendum, recall, or nomination
petition or any other petition.
(b) Solicit a vote or speak to a voter on the subject of marking
his or her ballot.
(c) Place a sign relating to voters' qualifications or speak to a
voter on the subject of his or her qualifications except as provided
in Section 14240.
(d) Do any electioneering.
As used in this section, "100 feet of a polling place or an
elections official's office" means a distance 100 feet from the room
or rooms in which voters are signing the roster and casting ballots.
Any person who violates any of the provisions of this section is
guilty of a misdemeanor.
http://www.snopes.com/politics/ballot/electioneering.asp