Invisible Unit Indicator?

Just recently I played an ARAM game as with a on the enemy team. My bought an oracle item so all was well, but I noticed something odd towards late game when decided to try stealth tactics and ambush any of us when we were low. I checked the entrance corners of the enemy's base with my Q and W to look for him and noticed a red arrow flash under my character model that pointed me to were my W had apparently hit . Unfortunately the game ended before I could test it out again. I wasn't aware of such a thing existing in the game. If anyone could enlighten me that would be appreciated.