I'm fairly certain he's not worried about the guy with him. He might be more concerned with the upscale areas around most airports.
Carrying a firearm legally is not an irrational or evil act. It's a decision. One makes to protect themselves since the police have ZERO duty to protect you thanks to multiple SCOTUS rulings over the last few hundred years.
OP: Depending on the state laws a "no guns" sign may or may not carry any legal weight. Carry legally and remember: "Concealed means concealed".