Instead of a signed release, in recent years I'm seeing posters saying that if you walk in an area you consent to the commercial use of your likeness for unlimited purposes without payment. At least once, I've seen this on a public sidewalk, it wasn't clear where one might walk that would be subject to this release by poster, and the release purported to apply to unaccompanied minors. The language was written the way lawyers write. If the company was smart, they had a video camera to record who saw the poster in case of a lawsuit later, but I doubt most of the companies bother. No one talked to me about it. Since a person reading the poster and walking in the intended area does not thereby receive consideration, there is no contract.
I wonder if this has wider implications. Suppose I have a house for sale and it has a walkway to the front door. Could I put up a poster saying that if you walk on the walkway you bought the house, including a mortgage with an interest rate I set, and would the poster be binding? Could I create a website offering website design services with my email address and say that if you email me that constitutes your buying my high-end service as soon as I access your email? Could I paint a poster on the side of a truck with a camera and photograph two million people and say that here are two million identifiable people every one of whom loves my brand of soda and urges you to buy a case? Suppose a park is frequented by published writers, musicians, artists, and inventors of some repute; could I put up a poster by which I acquire all of their intellectual property because they happen to be in the park? The possibilities of consent by poster seem infinite.
Or, although I've seen posters like this for at least 5-6 years (one back then was in a business location open to most of the public), has this never been tested in court and is the poster system probably not a valid substitute for a signature, even for mentally competent English-fluent adults not in a rush and allowing that certain contexts wouldn't allow it (e.g., civil court settlements and plea bargains couldn't rely on the poster system)?
Or if you didn't have a reason to read the poster (surely no one has to read every writing that's visible) and simply walked through the area in question without reading it you're not bound by it but someone who did happen to read it must accept its terms?
If the geographical boundaries are unclear so that reading the poster gives you no clear remedy by walking away, does that change the law on the validity of consent by poster?
Website terms often say that using the website constitutes consent to the terms and often reading the terms to discover this requires using the website before you start reading, but I doubt that's legal consent, but maybe consent will be found after you've read them and didn't try to revoke consent, e.g., by not using the site any longer.
In the United States, this all might well vary by state and may depend on common law.