Ok so this isn't much and most people would say I was dillusional, but this legitimately happened to me. Though anything that may explain this was supposedly removed from minecraft, this still happened. Now to the story.

I was playing on my own custom server, setting it up for a couple of my friends and I to play on. I had built most of the first town and was working on the spawn to get an automatic replay for disks. I had a TV looking thing set up in the house right next door, with black wool as the screen, oak wood stripe as the base and two noteblocks as the end piece for the base. As I was putting the finishing touches on the auto replayer, I heard the door to the house open then a note block get played about halfway through it's entire spectrum. I had my chat disabled so I figured my friend had joined and I missed, so I sprinted over to see for sure. There was nothing, I held tab and I was the only one on. I re-enabled chat and saw the several error messages from my commands, but no 'player has joined' or 'player has left' messages. The only programs I had up were Minecraft and Skype. I wasn't in a call and had it on DnD so I wouldn't get message plings. The scarier thing is, I made a road to a second town and stopped in my tracks. What I saw convinced me to close minecraft, save the server and close it. I sat for a couple seconds taking deep breaths then went here to post it. What did I see? It was a sign. It had the words "I'm watching" and nothing else. The worst part of this whole endeavor, I went on later and tested the automatic disk replayer, just to find out that hoppers can't put disks in jukeboxes.