Bold obvious advertising is NOT invisible. The goal is to increase awareness of a brand.
But less obvious, even invisble persuasion methods such as PR (public relations).
Social media which connects people in a network sells products and ideas even more subtely. Sometimes the con artists don't even know they are doing the conning.
Consumers have grown immune to big budget advertising, but marketers that expend a bit of time and effort — rather than piles of money — can generate effective results with inexpensive, small-scale stunts.
Here is a "gallery of guerrilla and street marketing examples". And a non profit example.