If you are sending Casascius Coins internationally the best way for you to label them is;
"Collectible Token"
Using the words coin, Bitcoin, or anything like it is a sure way to have your items held in customs and either returned to you or confiscated. Those terms refer to money and/or legal tender. Typically you're prohibited from shipping such items internationally.
I use the term Collectible Token and it works well.
Also, put "Contents: Less Than $XX USD". Make the number as small as possible, but don't go too far. For example, you'd be fine sending 2-3-MAYBE 4 coins and declaring the value as $15-20. Why is this important? Stupid fucking excise taxes. They are there to "protect us". Basically, they tax you for goods you bought abroad that you could have gotten at home. Although, this does not ALWAYS happen. Anyway, its good to be safe. $1000=MUCH higher excise tax than $20=. I trust you know what I mean!