The AP story is here. The Democrats’ claim is that posting the notices would constitute illegal electioneering. I’m not convinced. According to the AP story, “The notices also would let voters know that a vote for Tim Mahoney, Negron’s Democratic challenger, will count for Mahoney and a vote for unaffiliated Emmie Ross will count for Ross.” Not only does it not sound like these notices are not electioneering favoring Joe Negron, Mark Foley’s replacement. It also makes good sense. The Florida legislature has adopted a law for replacement candidates that is likely to confuse voters. Posting these signs would seem to alleviate some of the confusion (though I’d predict not enough to allow Negron to win in the district).
UPDATE:
The statutory anti-electioneering rule appears to be the the following:

102.031 Maintenance of good order at polls; authorities; persons allowed in polling rooms and early voting areas; unlawful solicitation of voters.–…
(4)(a) No person, political committee, committee of continuous existence, or other group or organization may solicit voters inside the polling place or within 100 feet of the entrance to any polling place, or polling room where the polling place is also a polling room, or early voting site. Before the opening of the polling place or early voting site, the clerk or supervisor shall designate the no-solicitation zone and mark the boundaries.
(b) For the purpose of this subsection, the term “solicit” shall include, but not be limited to, seeking or attempting to seek any vote, fact, opinion, or contribution; distributing or attempting to distribute any political or campaign material, leaflet, or handout; conducting a poll; seeking or attempting to seek a signature on any petition; and selling or attempting to sell any item.

I don’t think that the statute should be interpreted to apply to information provided by elections officials. A sign posted by election officials regarding the effect of the vote should not count as “distributing…political…material.” Indeed, to read the statute as barring such information would render invalid the following other two Florida statutes:

101.031 Instructions for electors.–
(1) The Department of State, or in case of municipal elections the governing body of the municipality, shall print, in large type on cards, instructions for the electors to use in voting. It shall provide not less than two cards for each voting precinct for each election and furnish such cards to each supervisor upon requisition. Each supervisor of elections shall send a sufficient number of these cards to the precincts prior to an election. The election inspectors shall display the cards in the polling places as information for electors. The cards shall contain information about how to vote and such other information as the Department of State may deem necessary. The cards must also include the list of rights and responsibilities afforded to Florida voters, as described in subsection (2).
101.5611 Instructions to electors.–
(1) The supervisor of elections shall provide instruction at each polling place regarding the manner of voting with the system. In instructing voters, no precinct official may favor any political party, candidate, or issue. Such instruction shall show the arrangement of candidates and questions to be voted on. Additionally, the supervisor of elections shall provide instruction on the proper method of casting a ballot for the specific voting system utilized in that jurisdiction. Such instruction shall be provided at a place which voters must pass to reach the official voting booth.

Thus, the Florida scheme as a whole seems to recognize both a “solicitation”-free zone at polling places as well as the responsibility of election officials to provide information to voters. Such information, however, cannot have a partisan cast. Cf section 101.031(4) (“(4) In case any elector, after entering the voting booth, shall ask for further instructions concerning the manner of voting, two election officers who are not both members of the same political party, if present, or, if not, two election officers who are members of the same political party, shall give such instructions to such elector, but no officer or person assisting an elector shall in any manner request, suggest, or seek to persuade or induce any elector to vote for or against any particular ticket, candidate, amendment, question, or proposition. After giving the elector instructions and before the elector has voted, the officers or persons assisting the elector shall retire, and such elector shall vote in secret.”)