Education is awesome and all and the general population does need to know more about Sikhism, so these signs do have good intentions. But I do feel weird about this.
I'm assuming that the Sikh taxi driver was beaten because he was mistaken for a Muslim and retardly assumed to be a terrorist. The reason I assume this is because many Sikh people were physically/verbally harassed and even killed post 9/11 because they wore turbans/paghs and called terrorists. The reason why I feel weirdly about this is because it doesn't stop the underlying cause for the violence - straight-up ignorance. Not ignorance about Sikhism, but ignorance in that people assume that just because one person commits acts of terror in the name of their religion, that all people who identify themselves under that religion are just as guilty.
A guy will ill-intentions gets into a taxi cab with a Sikh driver. Assumes that because he wears a turban, he is a Muslim and thus a terrorist. He is about to do something stupid, but then reads the Sikh signs. He realizes that his driver isn't Muslim and probably not supporting a terrorist cause. Nonetheless, the problem is not solved, just misdirected. If he meets a Muslim guy or realizes another taxi driver is Muslim, he may still act on those ignorant impulses. In the end, it helps Sikhs from being mislabeled, but hate crimes will still be committed. If not against Sikhs, then against Muslims or any one stereotyped to terror.
I don't think it helps the problem at hand much because it doesn't target the main cause. It has GOOD intentions and the general public will become more aware about Sikhism, but I think it will do very little to reduce the hate crimes that seemed to prompt the student to start his work.