Advertising is cheap, these days, because no one can afford it. Because of this a lot of public interests and charities are buying advertising space.
The London Police Department recently started running an ad on bus shelters saying “Anything you say can be held against you”. It’s just a big sign saying that. It’s creepy. However, creepier is the other advert which they’ve put up on other bus stops saying “You have the right [not] to remain silent”. Thank you for the information, police.