Quoted from TDK-WPG:

As a teenager I was an audio nut (had more time then) and was fascinated with the TDK MA-R cassettes. They were unique in that they had metal reinforcement as opposed to being all made of plastic. In theory that was supposed to make them a more “audiophile” product but the cassette never came close to the audio quality of my old reel-to-reel. Cassettes were much more convenient in the car though!
TDK became my nickname through high school, and thus my arcade initials. My avatar is an image of an MA-R I found on the internet.
Useless movie trivia: in Terminator, Sarah Connor uses an MA-R to record her message to John Connor, her unborn son. IIRC, they screwed up and then used an SA later in the same scene, instead of an MA-R, but I may be wrong about that.