Have you been having a lot of Romney/Ryan signs being stolen in your neighborhood? We have where we are in Miami. Interesting that the ones stolen have been at houses near a local elementary school. Houses with signs farther away have not by and large had a problem (And I don’t think it’s the kids doing it.)
Put a couple signs up facing the street. Liberally smear some roofing tar ( or dog crap if handy ) on the back of the sign near the top.
When they run up and grab the sign it will get all over their hands, which they will immediately rub on their pants, not knowing what it was.
One treatment cures most sign thieves for life, especially when they have to get back in their car covered with tar or dog crap!