I've heard that the original owner of SOB actually owned the land where the billboards were placed. As operating/maintenance expenses grew for SOB, he would sell off more and more of the billboard locations, which is why you don't see as many billboards now as you did years ago.
Also, this may also be a untrue tale, but I've heard this, too: he was originally an unwelcome business owner in those parts of SC, mostly from the folks in NC; they felt that he was "stealing" customers from their own businesses.
The SOB owner made his point of being a savvy business owner by paying his staff with only $2 bills. When those $2 bills started showing up in huge numbers in the community, the other business owners realized how much revenue was being generated by SOB, and how much influx of money was being introducted into the area, that they then gladly welcomed him and SOB.