Photo via hollywoodwheels.com.
Porsche’s company logo was based on the coat of arms of the Free People’s State of Württemberg of former Weimar Germany. As the cars were made in Stuttgart, the Stuttgart coat of arms was placed in the middle as an inescutcheon.
In 1952, Xaver Reimspieß, who is also said to have designed the Volkswagen logo in 1936, sketched a crest that symbolised the roots of the company. The design is still used today with just a few minor differences in detail.
Here’s an interesting short video showing how the Porsche bonnet badge / hood emblem is handmade.
The current Porsche logo.
The original Porsche crest as a quality seal, on porsche.com.