This symbol means that you have an event on that object in domain model.
It inform you that commit of that object will trigger an event action.
On creation of that object you can choose on option commit – “Yes without events”. Then you will get differnt symbol, that will inform you – there is an event on that object in domain model – but it will not be triggered.
You should see that symbol also in domain modal, close to name of that entity. Every entity with event should be marked that way.