Since the state needs money here is a way to generate revenue (
keep in mind I have read too may FLL posts 
)
The state (or towns) could collect all signs left up past the time allowed by law and "redeem" them, perhaps charging candidates $20 per square foot for the total footage "redeemed". Example, 100 signs collected, each 2 square feet equals 200 square feet times $20 equals $4,000 owed by the name on the sign. Maybe the "cost" would encourage them to remove them rather than paying to have them "redeemed".
