That's an Amateur Radio Call license plate and those were my call letters back in the day. I predicted my lifelong broadcasting career a bit early when I became a "ham" radio operator.
Here's a picture taken in one my many ham shacks over the years. I got my first license in 1955, as a 15 year old boy and held a series of licenses over the years. I think this particular scene was in the basement of our family home in North Dakota though I can't be sure. I've always been amused by the photo because it has all the air of a spy in his den in World War Two, getting some bombing coordinates to his confederates in the Allies.
'Course, I've always had a vivid imagination, too.
