Steve Hoefer, who has contributed several articles to MAKE, including the Secret Knock Gumball Machine and the Tacit Ultrasonic Bat Glove, has a good post on his blog about how to bring your electronics projects on flights without running into hassles with the TSA.
Communicate, don’t try to hide. This is what a TSA inspector sees when they open my luggage:
Clearly labeled and organized things, a concise letter to the TSA inspector, contact information (business cards inside of each box too). And a copy of Make magazine for good measure. The outside of my luggage is covered with high visibility retroreflective tape. It’s not trying to blend in.
Front and center is a clear, concise note for the TSA agent explaining what they’re going to find within. It doesn’t have to be complete, and shorter is better. But it shows you care about the same things that security agents care about. You’ll also notice that all of my crazy crap prototypes and tools are right on top where they’re easy for an curious inspector to look at. They’re labeled with what they are. I have my contact information prominent and in each box, just in case something gets mislaid.