Guerilla Advertising

Guerrilla Advertising is advertising designed so that the target audience is left unaware they have been advertised to, while leaving the desired impression of the product.

An example of this is a cellphone company hiring attractive young people (agents) to walk around asking people to take pictures of them with their new camera-phone. If the person who takes their picture remarks about the phone, the agent will recite a sales pitch under a pretext similar to "I love this phone and use it EVERYWHERE!"