I don't know about where you live, but here in WA there's a pretty stiff fine for stealing those signs. It seems that the folks running for election were faster in putting them up than taking them down, so people started swiping them for various purposes ('Yard Sale Today' was popular). They are said to cost about $15 each, so they didn't want to lose them.

I've never seen any shelters made from them, but who knows?

Sue