In 1971, Adidas released their new trefoil logo - just in time for the 1972 Munich Olympic Games - and the logo was used as the exclusive logo of Adidas until 1997. The trefoil logo can be viewed below; in the numerous configurations it has been released in.
Standard Trefoil Logo (with two stripes)
Trefoil Logo in different configurations (no stripes, one stripe, and four stripes)
The trefoil logo was developed in the early 1970's to combat sportswear companies who were releasing products that were using designs similar to the Adidas three stripes design. Adidas needed to differentiate their products from the look-a-likes and the best way to do so was by stitching a Adidas logo - which was a registered trademark - on their products. The trefoil logo was trademarked, therefore, it could not be used by other sportswear brands.
The trefoil is still being used by Adidas, but it is now only used on 'Originals' products; the performance logo is used on the majority of new Adidas products. The change of the logo was inspired in the 1990's when Adidas decided to divide it's products into three categories: 1) Adidas Performance; 2) Adidas Originals; 3) Style Essentials. The new Adidas logo would be used by Adidas Performance and Style Essentials products.
Separating Adidas products into three categories was no accident: it represented the 'three stripes' of Adidas: the classic design that has been used on the majority of Adidas sportswear and sneakers since the early 1990's. Adidas changed their company slogan - in the 1990's - as well as their logo: the trefoil logo was associated with the slogan "Impossible is Nothing", and the new Performance logo was associated with the slogan "Adidas is all in".