SteveBasedGod

So i setup a mob grinder spawning slimes and i threw in zombie pigmen to grind gold and i came back after a little while to check the chests and i found a random enchanted sign with sharpness 4 knockback 2 and fire aspect 1 and +10 health when you are holding it in your hands. It is jsut a normal sign from minecraft with enchants and health when you mouse over it. Any idea what mod makes these drop? What mob drops them? What the rate is?