The little pocket found on blue jeans was traditionally introduced to protect pocket watches. Today, many jeans are called five pocket jeans, but jeans were traditionally manufactured with only four pockets. There were two pockets in the front, the small watch pocket and one pocket in the back.
With the popularity of pocket watches fading, the small front pocket has taken on new names, including a coin pocket, ticket pocket or trinket pocket. This pocket is small and tight, protecting tiny trinkets and coins from falling out, even in the wash. Many fans of vintage blue jeans like this tiny pocket for the worn look and feel it gets.