I'd prefer to make a more forceful case that there are limits to contracts, and not to rely on the technicality of people saw the note, or if "a meeting of minds" actually happened.

What if the note is also in the actual contract that has my signature? Is the content of such contracts limited in any way?

I mean – it must be. I can easily get any number of people to sign contracts that include a right for me to their firstborn child.

Whatever legal doctrine courts would use to strike down such a provision should also apply to, for example, people waving their right to sue, to freely discuss the content of broadcasts, to rate the product/service being purchased etc.