pashute yid
funny you mention about bobby pins in yarmulkas. my nephew was at my house the other day and asked me for a pin. i asked him for what, he told me to keep his yarmulka on his head. honestly that was never a problem before so i asked my sister why all the sudden he wanted one. she told her son “are you a leader or a follower?”
basically this new bobby pin/clip shtik is some guy decided to bring it in style.
and yes it is wrong for a school to put such a sign up, but maybe this rosh yeshiva wants his talmidim to be leaders and not followers.