A logo uses a picture, a name in a distinct font, or an abstract figure to represent a company, brand or product. Companies with world-famous logos include IBM, Pepsi and Shell Oil. Using a logo has clear benefits.
A well-designed logo catches the eye and identifies the company without the need for analysis or reading. When you see the yellow "M" known as the "Golden Arches," for example, you do not need to think or read anything else to recognize it as the fast food chain McDonald's. When you see a white, lowercase "f" in a blue box on your computer screen, you know instantly it's Facebook.
Good logos "go viral" -- people know the logo and its associations so intimately that they start to use it themselves to make a statement. In the early 1990s, for example, teenagers got Nike "swish" tattoos. Men photograph themselves with the Calvin Klein label of their underwear visible to tell others they have class and sex appeal.
Logos take an element of a company or product and make it appealing to its target audience. In the United Kingdom, for example, the Conservative party unveiled a new logo in 2006 that used the color green and the image of a tree to appeal to an environmentally conscious new generation. The Toys"R"Us logo uses bright colors and a bold, rounded font to appeal to children.