This mentions OverPassTurbo having a couple of icon sets. I’m not really sure how they work though. Except it doesn’t sound super intuitive. Another thing you could do besides icons is make the POIs load as different colors depending on the tags and sub-tags. You can kind of see an example of that with how the Name-Suggestion-Index color codes POIs based on if they are mapped with brand tags or not. As another option you might be able to load a different map style then the main one in OverPassTurbo that displays defibrillators. I think you do that by clicking settings, scrolling down to Tile-Server, and entering the URL of the map. I’m not really sure how that works though 
I’m sure there’s other ways you could do it. I thought there was another way to load custom icons besides how it’s done in the first link but I can’t find how to do it 