Questions about shipping firearms?

I want to sell a rifle of mine for some extra money. I will try selling it on Gunbroker and I'll have to ship it. I know it needs to go through an FFL, but I had some questions about the box I'm shipping in. Does it need to be marked as a rifle? I've heard in some places not to leave any hint that its a firearm, but then I've also heard its illegal to not have it marked. I want to follow the laws and do it right.