The logo of a company is a trademark that links the company to its products or services for the public. We can also term the logo as the branding of a company. The public would not have been able to differentiate between companies had it not been for these brandings. If a logo is designed effectively, it can successfully convey the one of a kind distribution proposition of the company and thereby promote it in the minds of the common mass.
There can be no better way to assess the effectiveness of logos than examining their evolution as time progressed. Starting with Microsoft the logo has changed from a 4 pane window with a black frame in 1992 to just the 4 windowpanes in 2001 when XP was released. Moving onto Volkswagen, the VW logo constituted of a circle with bumped teeth that made it look like a gear, and long arms circumvolving the circle in 1939. In 2000 however, both the gear bumps as well as the arms were removed and the logo was given the blue-silver colour as we see today! The thick tick mark that we see as the logo of Nike today previously used to have Nike written with it but was later removed. Refer to the info graphic for more interesting logo evolutions!