In riot's most recent attempt of punishing toxic play and attempting to reward players following the Summoner's Code, they have implemented warnings for players who have contributed to bad behavior.

Now, when a player receives a warning, it'll end up looking like so:


Here's a statement from RiotLyte on the matter:

Hey Summoners,

In a future patch, we'll be releasing a feature called Behavioral Alerts. This system will detect spikes of negative behavior (i.e if a player is having a particularly bad day or week) and fire an in-game client warning to the player; we hope that these alerts will give players appropriate feedback about their behaviors before they travel too far down the negative path. We believe that these warnings will prevent a significant number of people from ever being punished by player behavior systems; more importantly, we believe that these warnings will make a difference in the large number of Neutral and Positive players that have rare bad days of toxicity, but previously never got feedback to nudge them back towards the positive.

Full statement - Riot Games