This way police is free to handle actual crime.
Suppose I were operating such a business with legal advertisements only and the detective asked me "Hey I saw a sign on a telephone pole saying you buy houses for cash, is that right?" why would I answer in the affirmative?
> "No, it's weird that you saw that. I don't post signs on any telephone poles, this is a highly reputable business.
They'd only say that if they're smart. Many of them probably aren't, and their guard will be down if the detective can do a passable "desperate alcoholic" impression over the phone. But regardless, I agree that false negatives are more likely than false positives.
"No, it's weird that you saw that. I don't post signs on any telephone poles, this is a highly reputable business. However, as long as you're here, I definitely do buy houses for cash, and it sounds like you're interested in that."
https://www.sciencemag.org/news/2019/06/psychologist-explain...
If I didn't advertise on telephone poles but somebody else was trying to frame me, and then I proceeded to act as though those signs were my own, then why would I not deserve punishment? If those signs advertised my business and I neglected to disown the signs because I was greedy, I think I'd deserve to be fined by the city. If I admitted on a recorded telephone call with a detective that the signs were mine, even if they weren't, then I've screwed myself with my own greed, which is fitting and just.
If a detective merely asks you "do you post signs with your name and number with an offer to buy houses", a lot more steps have to take place before reaching the point where you, personally and individually would see a fine for what is in more cases than not going to be a civil infraction that I would imagine, one can take photos of, go to your municipality and contest and say "those signs are illegal but are not mine, these signs are legal and belong to me".
You're missing the point were the detective specifically asks you if you placed signs on telephone poles and got a voice recording of you admitting you did place illegal signs. The real reason this doesn't happen is simply because detectives can't be bothered, not because it's an impossible case to make in court.
And because it's highly improbable that "yes, those are my signs" over the phone is enough to result in an infraction if they did.
Chances are, you're not even going to get the phone call in the hypothetical you're propping up, even from a clerk's office. If your name and phone number is on it, you'll likely just end up getting it in the mail without even the courtesy of a phone call to ask how your morning is going.
The possibility of a false negative does exist, but the possibility of a false positive seems greatly overstated and I do not believe aversion to false positives motivates the lack of enforcement as was suggested above.
While I'm at it, I leave your business card at the scene of a heist.