Pretty passive aggressive.
You have to figure if someone's wearing shoes outside of a work area (where it's necessary for safety) it means they don't trust you enough to let you see their socks/feet or to not step on their toes, but they won't just come out and tell you they don't trust you, instead they'll leave little signs scattered around like that.
That's why if you ever encounter someone who wears regular shoes around the house, you should be wary.