StogiusThere should be no problems at airports. I have never been stopped or questioned, most TSA people have no idea what it is and wouldn't even recognize it as being tritium. Even if they knew, it is not illegal to carry it.
StogiusThe short explanation of tritium legality: If you own a large amount (exit signs, stuff like that) it needs to be registered. You can't sell it for frivolous purposes in America, and you need a license to sell it for nonfrivolous purposes. The tiny amount in a vial, no one cares.