This is a 2-1/4-inch pinback button (as shown).
¡No Yo, Nosotros!! (210c)
...on the button's "curl" (either upper or lower edge, just outside the face of the button that's visible when it's viewed from the front). In 2016, for purposes of selling buttons at Dem-Party-sponsored events, this was usually* considered an acceptable alternative to having a union "bug" on the button. Hopefully this will continue to be the case in 2019 and 2020 (although as devoted as the Dems are to suppressing/silencing us Bernie folks, who can say??!).
* Of course, in the final analysis it depended on the personality of the event organizer. But most of them eventually concluded that, in the absence of a volunteers' union (LOL), they'd concede the validity of LABOR DONATED as an option.