A lot of native actors of Unreal has an icon (gismo) that is shown on the viewport. Example: A "Point Light" has a light bulb, a "Player Start" has a joystick and a flag, a "Sphere Reflection Capture" has a metalic ball icon and so on.
Print screen of the mentioned icons:
How to replicate this behavior to my Blueprint Class
(let's assume my parent class is Actor
if it make easier)?
Is there a way to create my icon (as .ico or .png) and use it to represent my blueprint in viewport?
You can add a "billboard" component to your actor. By default it will be "hidden in game" to be visible only in the editor.