Keep in mind that marketing is not just trying to teach you about someone you're unaware of, but is also in part about assuring you (and your boss) that you're about to make the right choice when their sales team is already talking to you, and even in part about ensuring that you (and your boss) continue to feel confident that you did make the right choice (or alternatively make you have doubts about having picked the competitor) after you made the buy.

Making their sales peoples job easier, in particular, can be a lot cheaper than getting the marketing on its own to sell someone on you. They want you to go "oh, yes, FooBar Inc, I recognise that name" instead of your reaction being "who?!?".

A lot of marketing without calls to action fall in the latter two categories. In that case they don't need to tell you who they are. They just need you to notice that they're there enough that they seem like a player that is a good choice. You don't even necessarily want to come across as caring too much about explaining who you are - you just want to portray the silent confidence of someone buyers should already know.

(I have no idea whether the specific billboards you're talking about succeed at this)