Almost worse (as it is always for dumb ideas of this kind) is the enforcement. Are we going to have a whole system of definitions of what is billboard (when is it just a poster), jurisprudence, inspectors, etc. The kind of 0th order thinking of '"they" should ban X' has no relationship with reality, even if it sounds like a good thing if you dont think about it (personally I hate advertising) This is the same class of stupid idea that makes no practical sense that we see in various populist political campaigns
Edit: I have to admit, I didn't anticipate so many seemingly angry (and condescending - the guy talking about animal cruelty laws and "we encode complex things...", lol) replies. Anyway, the above is just my perspective, I guess if you want your tax dollars working towards something like this, there is a pathway to a billboard free future