10 most difficult logo riddles

The origin of the logo may be traced back to a trip made by the 22-year-old André Citroën to Łódź city, Poland, where he discovered an innovative design for a chevron-shaped gear used in milling. He bought the patent for its application in steel and started his company which initially produced gears.

Auto Union was the predecessor of Audi. The car was extremely difficult to handle, but its tremendous power and acceleration were undeniable - a driver could induce wheelspin at over 100 mph (160 km/h). Silver arrows of Auto Union and Mercedes Benz dominated car racing until the outbreak of World War II.

Charles Goodyear for many years improved the method of hardening the rubber. When he succeeded in 1839, investors were already offended by earlier failures. Charles died in misery. The Goodyear company was named in his honor, but otherwise is not related to him.

Founded in 1976, today Acer is one of the world’s top ICT companies and has a presence in over 160 countries. As Acer looks into the future, it is focused on enabling a world where hardware, software and services will infuse with one another to open up new possibilities for consumers and businesses alike. The etymology of the company's name comes from the Latin word "acer" meaning "eager, vigorous, ".

The brand was founded by the Spaniard Enric Bernat in 1958, who started his business in Catalonia. It is currently owned by the Italian multinational corporation Perfetti Van Melle.

The city of Sedona in Arizona mixes the yellow M with rock around it to make it turquoise. Officials in Sedona, Arizona told the fast-food giant they were unable to open a restaurant with the trademark yellow logo. This is due to the city's strict regulations which prevent buildings from ruining the picturesque view of the desert.

The Copenhagen Metro is a 20.4-kilometre (12.7 mi) system opened between 2002 and 2007, and has two lines, M1 and M2. The metro has 22 stations, of which nine are underground. In 2016, the metro carried 61 million passengers.

HTC was founded in 1997 as a manufacturer of notebook computers. The company changed name to HTC and doesn't use "High Tech Computer" name any more. However, some HTC smartphones are still visible as "High Tech Computer" devices when plugged into a PC.

The origin of the logo is often thought to be a portrayal of the movement of an aircraft propeller with the white blades cutting through a blue sky. However, this portrayal was first used in a BMW advertisement in 1929 - twelve years after the logo was created.

The client application was created by WhatsApp Inc. of Mountain View, California, which was acquired by Facebook in February 2014 for approximately US$19.3 billion. By February 2018, WhatsApp had over one and a half billion users, making it the most popular messaging application at the time.