Guerrilla Advertising

As part of my London Brief I looked at Guerrilla Advertising, a lost cost advertising strategy that covers various mediums such as graffiti, stickers, flash mobs etc. During my research I found a news article which talks about a new craze to hit the London Underground, in which people have been using this form of advertising to create humorous stickers. The stickers were placed across the underground covering up or replacing signs. Some people argued that it was vandalism or a hazard, however I think it's quite an entertaining fun idea and defiantly would brighten up peoples commutes into work etc. 
Some examples of the stickers: