Take it from the experts. Check out the definitive aikiweb "traveling with weapons" thread: http://www.aikiweb.com/forums/showthread.php?t=2219. Discussed are wooden practice weapons (bokken/bokuto) as well as (metal) iaito and katana.

A couple of highlights:
- PVC tubes are cheapest and safest, you can use the bubble wrap inside.
- Using the actual term "weapons" is often not a terribly good idea as it can set off all kinds of reactions. At the very least, substitute "martial arts equipment" or "katana".

That said, things can still go wrong no matter what you do and how you describe it. Friends tried to UPS my weapons to me transatlantic from SFO three years ago to save me trouble (seeing I already had two pieces of checked baggage) only to have UPS return the package to them twice! Their justification was some BS along the lines of, oh no, weapons, what an unreasonable thing to try to send. Mind you, this was not an actual sword, just the wooden stick and sword (jo/bokken)! As a result of this, I am now keeping three sets of weapons in three different countries..