Sign theft and vandalism continues to be a problem in some areas. District Attorney Michael Povich has issued a statement regarding this, which you can download from the HCDC homepage, or use this link.The statute:
23 MRSA §1917-A. Unlawful removal of political signsHope that's helpful.
1. A person who takes, defaces or disturbs a lawfully placed sign bearing political messages relating to a general election, primary election or referendum commits a civil violation for which a forfeiture of up to $250 may be adjudged.
UPDATE: Then there's this solution, from New Mexico.