We have lost five signs. The one last night had been covered with vaseline and my husband had attached it to metal fence posts. Meanwhile, our neighbor's Kerry sign remains intact. I hope that everyone who drives by takes notice. Even the fence posts were gone this morning and that took some time. It is creepy on a lot of levels, no wonder they like the LURCH.
Take joy in the fact that they got messy though. Just go out and put another one back up and put even nastier stuff all over it - paint, syrup, glue, anything that's sticky and messy. It's a given that they're gonna steal your sign so have fun with it and make them pay. I suspect chewed up bubble gum stretched over the stakes can also be fun, or just try the paint bag.
Add red pepper seasoning to that. They won't be stealing any signs in your yard again.