My anecdotal evidence is in accord with this.
During the last few months, I have let myself have a beard. I have a darkish skin, so with a beard I look very Arabic.
In my last flight, security were specially bothersome, making me open and show my luggage. I didn't relate it until my friend pointed it out, but I am very sure he was right now.
When traveling, he likes to wear a shirt that says "Italia" because when airline security thinks that he's Italian, he gets less hassle.