A huge distinguishing characteristic is that some of these things come to you, or are found passively, and some of them you seek out. I think that when the ad comes to you, there is a very good chance it has little or no value.

Job listings are useful, but I have to seek them out.

An event calendar is something I seek out.

Product descriptions are only shown to me when I seek details about the product.

An ad on the street is somewhere in the middle. For most people the acceptability of it is about setting (not in a nature park, please), and ignorability (LCD billboard vs. telephone pole flyer).

I think that is the distinction that people are making between marketing and what is being called ads.