I'm also having this problem at the moment. My package has not arrived yet, but I saw it had had this "Adult Signature" feature on the tracking info. It was shipped via USPS Priority.
The whole reason I do USPS is so I DON'T have to sign for it, but this is even worse. I already have nosy family members who like to ask what is in my packages. Having it require an "Adult Signature" is quite suspicious. So much for discrete. =/
I just messaged Stormy the info she asked for, hopefully the lovely folks in charge will figure this out soon. I'll be holding off on future orders for the time being until this gets resolved.