Riot Games announced that they are introducing banners featuring sponsor logos to Summoner's Rift, League of Legends' most popular map. These will only be visible to esports viewers though.
League of Legends has a much bigger audience than Dota 2 and yet Valve comes up with a much bigger prize pool for The International than Riot does for World Championships, year after year. Dota 2's ace in the hole is the battle pass that inflates the prize pool and LoL esports fans have been calling for Riot to introduce something similar or use more sponsorships so we can maybe see bigger prizes at Worlds.
On May 26, Riot announced that sponsors will get more ways to advertise their products in League of Legends esports. These ads will be visible on Summoner's Rift banners which can be found all over the map but there are a few things to consider.
First, the sponsored banners will not be in the regular game. In other words, players will not see MasterCard banners while trying to get out of Silver 3. Secondly, despite the sponsored banners appearing in esports events, the pro players will see Summoner's Rift as it is now, with the regular banners.
The only people who will see the sponsored ones are the fans who tune into esports event streams, such LCS, LEC, LPL and so on. It is probably some sort of overlay which doesn't appear to be intrusive during regular play but replays from different angles might put them in focus.
While some viewers might find this to be distasteful, it is not really different from the regular sports where we can see ad banners all over the stadiums.
There is currently no official confirmation from Riot on whether this will influence the Worlds 2020 prize pool.