A Coca-Cola advert from the 1890s.

Advertisement in a rail station in Berlin. Advertising is a form of communication that typically attempts to persuade potential customers to purchase or to consume more of a particular brand of product or service. Many advertisements are designed to generate increased consumption of those products and services through the creation and reinforcement of "brand image" and "brand loyalty". For these purposes, advertisements sometimes embed their persuasive message with factual information. Every major medium is used to deliver these messages, including television, radio, cinema, magazines, newspapers, video games, the Internet and billboards. Advertising is often placed by an advertising agency on behalf of a company or other organization.[citation needed] Advertisements are seen on the seats of shopping carts, on the walls of an airport walkway, on the sides of buses,and are heard in telephone hold messages and in-store public address systems. Advertisements are often placed anywhere an audience can easily or frequently access visual, audio and printed information.[citation needed] Organizations that frequently spend large sums of money on advertising that sells what is not, strictly speaking, a product or service include political parties, interest groups, religious organizations, and military recruiters. Non-profit organizations are not typical advertising clients, and may rely on free modes of persuasion, such as public service announcements.[citation needed] Advertising spending has increased dramatically in recent years. In 2006, spending on advertising has been estimated at $155 billion in the United States[1] and $385 billion worldwide[2], and the latter to exceed $500 billion by 2010. While advertising can be seen as necessary for economic growth, it is not without social costs. Unsolicited Commercial Email and other forms of spam have become so prevalent as to have become a major nuisance to users of these services, as well as being a financial burden on internet service providers.[3] Advertising is increasingly invading public spaces, such as schools, which some critics argue is a form of child exploitation.[4][5]