That's horrible. At my home we always have political signs up (our property is one of the prime spots to advertise) and we've never had a problem. My guess is that a bunch of homophobic highschoolers did that.
As a former sign-stealer (oh..I have some stories...) these are some steps to help your situation:
1. NEVER go for the cheap paper & wire signs, way too easy to steal.
2. Get the nice big plywood signs. When you run the stakes in the ground, use OLD stakes, you know, the ones with nails sticking out and the wood is very uneven. It hurts like h^ll to try to take one of those outta the ground. Plus they don't fit well in a car trunk.
3. If you can, do what my parents did. Plant poison ivy around where you're going to have the sign at and let it creep up the legs of the sign. 
4. Have those solar lights shining up on the sign.