I have absolutely nothing more than vague impressions to back this up but it seems that a disproportionate share of the billboards of in this town, particularly around Burbank and Hollywood, are dedicated to TV shows. Of course, LA is a trend setter and a lot of media writers are based here, but billboards seem an inefficient way of targeting a relatively few influential players.
I suspect that (if I'm right about the over-representation) there's a bigger factor that has nothing to do with maximizing corporate profits. Instead the objective is to maximize the profile and reputation of the executives running the networks. The target audience is colleagues and acquaintances and the purpose is to create the impression that the executives are successful and influential.
William Goldman once observed that studio executives would rather make big budget films even when low budget alternatives made more business sense because, even if the big films lost money, they still gave you something to talk about at parties. ("I just greenlit the new Hanks/Roberts project. How about you?") After reading that, a number of why-did-they-make-that pictures were suddenly more explicable.
Lots of business decisions make more sense when you apply this cocktail-party standard (including the majority of sports sponsorships), but I wonder if anyone has seriously tried to study and quantify the extent to which home industries of a region are over-represented in local advertising. If not and if anyone's interested, I might have some design and metric ideas.