Hi I'm an audio engineer :)
I know audio. I know how to capture and manipulate it. I know how sound travels through air as well as through cables. My ears are trained. I've used them to record music, mix music, edit sound for films, and to hold up sunglasses. I own a studio. I own lots of gear, and know the finest details about each piece. I am aware that this science is an art. I am aware of my clients needs, so I exceed them.
I also have a piece of paper that documents my degree in this field.