A subset of visitors to New York City looks, on the surface, just like the rest. Some are high profile, like the boxer this year, and the football player, and the Tea Party leader from California. They are joined by the anonymous: the military wife from Minnesota, and the hazardous waste expert. There was a minister, and a surgeon, and someone in pest control.

What sets them apart is what each brings along on a visit to the city. A handgun. The guns are legally owned, with the home state permits all in order. The visitors have locked the gun in a box and checked it at the local airport, as they were told to do by the airline. But for these visitors, the trip to New York will almost certainly end in handcuffs and felony weapons charges, and their flights home will leave without them.

“They’re so used to carrying it,” said Dennis B. Coppin, a lawyer who has represented defendants in airport gun arrests. He described clients who don’t realize that the laws of the state they are leaving do not apply in the state where they are headed. They had tried to do the right thing.

“They contact the airline and say, ‘I want to bring my gun with me. How do I do this?’ ” said Martin D. Kane, a criminal defense lawyer in Queens. The travelers are told that the gun must be packed, unloaded, into a preapproved lockbox.