Cryptic messages from the Post Office

Somebody found this USPS note on our front door, and no one knows who it could possibly be from. True, one of my housemates just broke up with his girlfriend. But it was hardly a bitter ending that could have inspired cryptic messages scrawled on official USPS delivery notices.

Under "Article Number(s) it reads: "Your game will be like saying: clean up your act and defeat the enemy."

Then, under "Notice Left Section" it says: "Guard your territory or basket."

We don't own any baskets, so this must largely be a symbolic statement. I'm just keeping my fingers crossed that this wasn't written by the postman.