i had a similar experience only herobrine was not there the story is i went out mining i found 4 gold and 5 diamonds and a sign that said HEROBRINE IS WATCHING YOU it was creepy so i thought ok thats creepy! then i found emeralds and another sign that said HEROBRINE WAS HERE then i went home curious when i went home my windows were broke so i screamed in real life and shortly after i saw HIM it was creepy so i ran and when i got back my items were gone so i was scared and a day later i found a letter made of glowstone it was the letter E but it was the last i saw of him for 1 year then i saw another letter and that was the last i saw of him