In Person Activism

No, it wouldn't work in the US. I won't touch on anything the other commenter said, they are correct, I'd just like to add a few things.

When I was a carrier, I used to open mailboxes and find basically those car windshield flyers sometimes stuffed in the mailbox. Since they weren't delivered by USPS, and don't have proper postage, we were technically supposed to and allowed to take them all back to the office. Once there, the original owner (so whatever business did these shenanigans) would receive notice from the Postmaster basically saying "You owe us $X amount in postage, and you can't have your flyers back until it's paid." It didn't happen often where I was at, and normally the business owner would just write them off and we'd throw them away.

The bigger issue I always had with customers was the "Current Resident/Postal Resident/Postal Customer/Etc" addressed mail. Yeah, it's a flyer full of coupons you don't want, and it doesn't explicitly say your name, but unfortunately, it is still addressed to you, so no, I can't just not deliver it or throw it away. I'd have customers get visibly upset that we kept delivering them, failing to recognize that they weren't the customer in that transaction.

Basically: USPS only delivers things that have proper postage paid, while mail delivery itself is a free service. So if you didn't pay the postage, you aren't the customer. So all those spam flyers and newspapers and crap that say "Current Resident" and all that, USPS was paid to deliver them, and would be breaking the law if they didn't. Is it annoying af? Absolutely, believe me, when I worked there, I would've preferred to save my back/shoulder and throw them out too, but that's not how it works, and people (not you OP) need to get over the entitlement mentality of "but I don't want them delivered to me!!!"

It cannot work in the US; but it’s also useless under US rules. That is, it is already illegal nationwide for anyone other than USPS to feed your official US Mail postbox. Some people hate the fact that this gives USPS monopoly power because UPS and FedEx also cannot put anything in your mailbox. But the upside is US mailboxes don’t get junked up by a leafletter.

So in the US, the only legal way for mail to enter your postbox is at the hands of USPS, which IIUC means only mail that is addressed to your address because I don’t think USPS delivers unaddressed material unless it’s actually from USPS. That also means junk mailers must pay postage. If the local pizza shop stuffs flyers in your mailbox, it’s criminal and actionable.

The “no marketing” tags that people put on mailboxes outside the US (e.g. Europe) is to cover situations where anyone can junk up your mailbox. Then the signage means (in effect) “no mail that is unaddressed”.

Of course junk /can/ be addressed to you specifically (inside and outside the US), but you wouldn’t want the postal worker making guesses about whether it’s junk, would you? So I think that’s always delivered.