You're kidding right? Everything you listed is being done with because of a motive where they stand to gain somehow. They are not providing a public service. While the definition of advertisement does include "just telling someone something", in practise in the real world, advertisements exist because someone has motive to make them because they stand to gain from doing so, where as "just telling someone something" is never called an advertisement it's called an announcement or a broadcast.
> - Asking customer to place yard signs on their property
They don't ask the customer to do so out of the kindness of their hearts, they offer a discount on the bill for doing so. Another way to look at that same situation, is, extortion - "run our ad on your lawn for a month or you'll pay more for this work"... And, the discount compared to the length of time they get an ad spot on someone's lawn is probably very much in the favor of the company. Charging someone more money unless they advertise your business, not out of satisfaction, but because the other option is to pay more, isn't very ethical to me, as the customer basically is given a choice that isn't a choice unless they want to knowingly spend more money for nothing.
> - Small businesses putting physical ads in other small businesses
They share ads between each other to try to leach of off each others customers. Maybe even closer to "participate in our shared cartel or we'll send folks to some competitor who does.". Either way, it's not being done to inform folks of something, it's being done to profit and these users are already out, spending money, and close by, so it's the cheapest costing acquisition funnel.
> - Printing shirts, hats, pop sockets, etc. . . and handing them out for free
That merch given out is paid for by the company's marketing budget and that's because what they are buying is ad space with potentially unlimited and extremely cheap display time. You see a nice company giving you a shirt for free. What they see is a sucker who is happy to become a walking billboard that will go to packed concerts, bars, tv shows, friend groups, etc for the price of a cheap t shirt and silk screen, for the life of the tshirt, gaining brand recognition if nothing else the entire time. Manipulating a person into thinking the free shirt they were given is ethical advertising when they are actually being used to freely advertise their brand, not something I'd consider ethical.
> - sponsoring local events/athletes/scholars
All done to get a giant banner on the fence of the field, have your branding stamped on every helmet, bike, bat, glove, shirt, said in every annoucement, etc. They aren't "sponsoring" those things, they are paying for advertising space, and saying it's not that isn't very ethical. They aren't doing anything for the good of the community, they are doing it for mindshare. Redbull on every extreme sport for instance.
> - Parade floats, community bulletein boards, festival/event booths
Parade floats are so the company gets a mention or airtime or mindshare as it passes by people. Festivals and event booths, please see my free tshirt reply. That booth they purchased or conference they sponsored is advertising budget and used to push their product on attendees.
- wrapping company vehicles
> I used to do fleet vehicles for corporations. Company branding applied to company fleets is not advertising. It's so when those service vehicles arrive to a customer, they are recognizable by those expecting them (UPS, FedEX, DHL, Geek Squad, etc). They inevitably get used to advertise, because of course they do, but the only thing they can do is steal mindshare and force through repeat exposure a bias for the company just because you see their name more often. It's manipulation, and hardly ethical.
I'm not going to reply to example after example. No matter the application, no matter they given benifets or percieved value you think they are giving, the end result is for you to give them money, and the fact that so many forms of ads exist that people don't see as exactly that, companies talking you out of your money or otherwise using you to make money (walking billboard), shows that it's not possible to be ethical advertising. Ethical advertising is build a good product, let it speak for itself by being a good product, and let happy customers spread word when they want to, if they want to, and for no other reason than because of the product they are impressed with. If you're not selling garbage, or shit people don't need, you shouldn't have to spend money to manipulate people into thinking they need it.