Actually, there is no significance.
The CBS outdoor plants are just like all the other outdoor plants out there: They want to do business! And, if you've got the money, they'll post your signage.
Same company...different management. And the outdoor people can't afford to run their plants like the network.
In an ideal free enterprise world, that's the way it would work. But CBS (or whatever its corporate parent is now - Westinghouse?) been ruled for years by the maxim of "we control the message and we won't put out anything out there to the public before it's reviewed to make sure its in accordance with our political agenda." That's just their corporate culture - regardless whether it's electronic media or billboards or whatever. What I'm saying is that this is a deviation from the "usual." It either means that the "usual" is changing with the recognition that we're about to enter a new era in Washington, or that some heads will soon roll in their executive offices.