The California Fair Political Practices Commission adopted a new definition of express advocacy and the commission’s press release on the matter is here.

Under California’s political law there are two types of speech: issue advocacy and express advocacy. Issue advocacy merely informs the public about matters unrelated to an election and are essentially unregulated. However, express advocacy urges a particular outcome in an election and is regulated. Individuals and groups engaging in this regulated speech must comply with state rules requiring periodic disclosure of where they received their money, how it was spent and identify within their advertisements that they paid for the political communications seen or heard by voters. This new disclosure applies to messages that appear during the final 60 days of an election.

More information is available here (scroll down to Item 16).

(2) A communication “expressly advocates” the nomination, election or defeat of a candidate or the qualification, passage or defeat of a measure if it contains express words of advocacy such as “vote for,” “elect,” “support,” “cast your ballot,” “vote against,” “defeat,”  “reject,” “sign petitions for,” or otherwise refers to a clearly identified candidate or measure so  that the communication, taken as a whole, unambiguously urges a particular result in an election.
(A) A communication, taken as a whole, unambiguously urges a particular result in an  election if it is susceptible of no reasonable interpretation other than as an appeal to vote for or  against a specific candidate or measure. A communication is susceptible of no reasonable  interpretation other than as an appeal to vote for or against a specific candidate or measure when,  taken as a whole and with limited reference to external events such as proximity to the election, it  could only be interpreted by a reasonable person as containing an appeal to vote for or against a  specific candidate or measure because:
(i) The electoral portion of the communication is unmistakable, unambiguous, and  suggestive of only one meaning; and
(ii) Reasonable minds could not differ as to whether it encourages a vote for or against a clearly identified candidate or measure, or encourages some other kind of action on a legislative, 12 executive or judicial matter or issue.
(B) The following non-exhaustive examples, referring to candidates or measures on the ballot in an upcoming election, illustrate statements that in most contexts would be “susceptible of no reasonable interpretation other than as an appeal to vote for or against a specific candidate  or measure:” “Smith’s the One;” “No Measure A;” “Rally ‘round O’Malley;” “Create jobs with  Measure X;” “Only Nancy Brown can clean out City Hall;” “Proposition 123 – your last chance  to save California;” “Joe Green will earn your trust;” “Bob Boone is an unqualified, special-interest puppet;” “Shirley Hall – bad for California, bad for you.”
(C) The following non-exhaustive examples, referring to candidates or measures on the
ballot in an upcoming election, illustrate statements that would be susceptible of a reasonable  interpretation other than as an appeal to vote for or against a specific candidate or measure:  “Assemblymember Nancy Brown needs to be tough on criminals. Call her and tell her to stand firm on AB 100;” “Poor children need a home too. Support the Mayor’s stance against more  budget cuts;” “Thank you, Supervisor Smith, for continuing to support our farmers.”
(D) Safe Harbor. A communication does not “expressly advocate” the nomination, election or defeat of a candidate or the qualification, passage or defeat of a measure, within the meaning of this regulation, if:
(1) It does not include indicia of express advocacy such as mention of an election, candidacy, political party, opposing candidate, ballot measure, voting by the general public, or  the character, qualifications or fitness for office of a candidate or officeholder, or the merits of a  ballot measure, and;
(2) it focuses on a legislative, executive or judicial matter or issue, either urging a candidate  to take a particular position or action with respect to the matter or issue, or urging the public to adopt a particular position and to contact the candidate with respect to the matter or issue.
(E) Rules of Interpretation. If a communication does not qualify for the safe harbor defined  above, the Commission shall consider whether the communication includes any indicia of  express advocacy, and whether the communication has an interpretation other than as an appeal to vote for or against a clearly identified candidate or measure, in order to determine whether, on balance, the communication is susceptible of no reasonable interpretation other than as an appeal to vote for or against a clearly identified candidate or measure.