The US Postal Service lists the import restrictions into most countries: http://pe.usps.com/text/imm/ab_toc.htm Just click on the desired country into which you will be mailing the seed. Bookmark this link.
I have always filled out customs labels tersely, though honestly. For seed, I indicate:
"Clean seed in transparent packaging Nicotiana spp."
So far, it has encountered no problems in international mailings to countries throughout the world.
Bob
Thanks Bod for the info this link is a keeper helps a great deal .
Bill