As per their religion, Sikhs can’t trim their beards. Many do — yes, but it’s akin to a sin — Sikhs are supposed to maintain the 5 ks all the time — wear their hair long (a la Samson) - meaning never trim the hair anywhere (neither on their heads or beards or moustachios)
I know the Sikhs have this rule of never cutting any hair at all. That is their choice to be made. But if they walk around American neighborhoods looking like this guy, with most of his face concealed, they will stick out and make people worried.
The smart thing to do is to assimilate, while in public, otherwise don’t complain.