Strange man going door to door?

This strange man came up to my door tonight and went "Hellooooo" in a singsongy voice. I thought it was my parents, so I peeked through the curtain. A black man stood at the door, wearing some sort of badge. He kept going dee dee dee dee. And when he saw me he said "Hello there", so I stumbled back in shock. I am sort of paranoid about this. I just have this strange, creepy feeling. What do I do?