Why "MK.K"? There is no direct answer.
My other options often became boring to me.
When I was creating my signature for my first passport, I wanted something that sounded professional.
When I found an option, I saw MKK. It interested me. I thought about the future and decided to insert it as my name, adding a dot to MKK.
Later, when I created another signature for my possible autograph, MK.K looked natural.