Even if you were to sign this pledge, ads aren't as simple as "I see, I buy". Lots of branding seems to be around changing your perception of or just making you aware of a company or product so that several months later, when you're purchasing something in that category, you'll think of them. You can't possibly remember all the ads you have or haven't seen, so trying to restrain yourself from buying products which youve seen ads for seems futile.