...instead of taking that 6K and investing it into his / her business and trying to look out for his / her employees...
Let me pitch it this way - and I know nothing about what business did this, this is just a hypothetical scenario - let's say the business that does this rents industrial equipment to construction companies. There are a lot if construction companies hurting right now, and a lot of people in the Oshkosh area who are not Obama supporters. You're not the only guy around who rents industrial equipment to construction companies, but now you're THAT COMPANY

If the billboard was near your location, you may have some new customers show up just to take a cell phone picture of the billboard and get a quote from you for their next job.
It's not like the business owner who put up the billboard burned $6k for nothing. It costs over $6k for a page ad in most magazines, this was a risky investment that appears to be paying off. Only the business owner really knows if this was worth the PR risk. I've got a friend who owns a company that repairs sewer lines who'd do something like this

He had a couple goofy park benches around Chicago, I forget the crazy slogans he had on them
