I suspect that that may be correct. However it could be possible that a viral and highly photogenic / shareable billboard could reach a wide audience. Basically if it won the viral lottery and got a lot of eyes on it.

Having said that, I think the idea is fun. And that is why I'm submitting a design lol (see below).

I think realistically nostr probably does need more targeted marketing, I would think more along the lines of building on what is already here: permaculture, homesteading, tinkering devs and builders, meshtastic. Sponsorship of people who are already aligned with values of the protocol, people more outside of the bitcointwitter bubble (I have previously suggested, jus as an example, someone like Jay Dyer).