In Princeton NJ, where we once lived, they have an ordinance that requires the campaign to remove all signs within 48 hours of the election. I seem to remember there was a significant financial penalty if they failed to do so. My neighbor ran for elective office and I helped him the day after election day to gather up the signs. Do not remember what the fee was, but it did do the trick.
If they were on private property these types of ordinances have been repeatedly found unconstitutional. If they were on public property they were illegally placed to begin with.