TTC interior advertising signs, or “car cards,” have served two purposes. First, they have been a source of revenue for the TTC. Advertisers have paid for space on streetcars, buses and subway trains to promote their products, such as clothing and foodstuffs. Second, car cards have been an excellent form of print public service announcements. Car cards have covered etiquette issues, advertised fare changes and new services, and aimed to raise public awareness on various topics. The designs reflected the best of commercial art of the era, and in some cases concepts and images were shared between transit agencies.