A rectangular label made of real or imitation leather or paper, usually sewn to the waistband above the right-back pocket. The label was first used by LS&CO in 1886. Already then it depicted the two horses attempting at full horsepower to rip apart a trouser in opposite directions.
The label usually has the brand logo, the jean serial number, as well as its size. In 1954, LC&CO substituted the leather label of the 501 for a paper version.
Source: Nouvelle de Nîmes Nº 5: The Denim Dictionary