What does Suspender Buttons mean?
Suspender buttons refer to the buttons sewn on the inner or outer side of the waistband used to anchor suspender (straps worn over the shoulders and used to hold up trousers) to the trousers. Most suspenders have one strap that attaches to the center of the back of the pants and two straps on either side in the front.
Heddels explains Suspender Buttons
The suspenders themselves have buttonholes at the ends of the straps that allow for easy attachment to the pants. Especially with high cut or loose fitting trousers where the use of a belt is not practical, suspenders allow for quick and easy wearing and removal of the pants.
Suspenders began to fade in popularity after World War I as men grew accustomed to military belts. In addition, men began wearing jackets and waistcoats less frequently and did not want their suspenders, considered a undergarment, to be seen in public. However, suspender buttons remained on jeans until they were replaced by belt loops in the 1930s.
Here is an example of denim with suspender buttons: