Saab has an aircraft heritage. As for Mercedes and Mitsubishi, their insignia have nothing to do with aircraft whatsoever, as a quick google search shows...
The Mercedes story:
Daimler had died in 1900 at the age of only 66 but his two sons, now managers at their father's company, remembered that he had once sent a post card to his wife on which a star marked the house where he was living in Deutz. He had commented that eventually this star would rise and shine out over his work.
The Chairman of Daimler took the idea up in June 1909 applied to use both a three-pointed star and a four-pointed star as trademarks.
Both applications were granted, but only the three-pointed star was actually used. It was placed at the front of the car as a radiator emblem. Over the years the star, which was also intended to symbolize the modernization of transport on land, water and in the air, acquired various additions and refinements.
In 1916, it was placed inside a circle which featured four small stars at the top and either the word Mercedes or the names of the Daimler plants in Untertuerkheim and Berlin-Marienfelde underneath.
In 1921 an application was made to have the three-pointed star in the ring patented as a radiator emblem and two years later this request was granted.
The Mitsubishi story...
Yataro Iwasaki, founder of the first Mitsubishi company, created the famous three-diamond mark by combining two images. He blended the three-stacked diamonds of his own family crest with the triple oak leaf crest of the Tosa clan, his first employer. This emblem is the source of the name Mitsubishi, which means "three diamonds."