We have contracts with two companies that buy space from us and resell it to others. My guess is you saw it in the slot that Outdoor Hub buys from us. That's the long ad (728x90 pixels) just above the posts.
The other has the two box ads following the first post in a thread. I've not seen any political ads in their slot but as the election draws near there will be more and more in ODH's spot. They are equal opportunity and take money from both the good guys and the bad. I find it kinda humerous that the dumocraps spend their money on sites like this where there is darn little chance of them getting a vote from the money spent.
Last election cycle there were a lot of political ads on the forums where political discussion was taking place.