A slight variation on Murray's approach - I return the film to a black plastic bag similar to what it originally came in before putting it into the box. That provides an additional margin of protection in the event some bozo tries to open the box. I have a N, N- and N+ box, and to differentiate between one and two stop compensation negatives, I have stuck small plastic 'bumps' onto the black envelopes - one for one stop negs, and two for two stop negs.
Originally Posted by MurrayMinchin
Finally, when traveling, I take along a roll of blue painter's tape that I used to wrap around the box before going through airline security. Obviously, that won't stop someone from opening the box, but it could cause them to stop and read the label on the box that declares it to be unprocessed film.