The name of the red tag sewn on Levi's jeans pocket since 1936 is the Red Tab.
Levi Strauss & Co. introduced the Red Tab on the right back pocket of its 501 jeans in 1936. The small folded ribbon was designed to make Levi's garments easier to distinguish from competitors, many of which were producing similar dark-denim workwear after the company's rivet patent entered the public domain in 1890.
The original tab carried “LEVI'S” in white capital letters on one side. That vintage version is now known among collectors as the “Big E” Red Tab. Beginning around 1971, the lettering changed to the familiar mixed-case “Levi's,” creating the “small e” style associated with later garments.
A common mix-up is confusing the Red Tab with Levi's other colored tabs. Orange Tab, SilverTab and other labels appeared on particular product lines or eras, but the signature tag introduced in 1936 was red. The tab was first used on jeans and later appeared on denim jackets and other Levi's products.