Question for Y’all

I have a question for y’all.  (I’m in my southern belle mode, because of the Atlanta series.  Forget that.  I’d actually rather not talk about these past four games.)

This photo is from the scoreboard at AT&T Park a few weeks ago.  Couldn’t “ML Service” and “ML Debut” mean “Major League” or “Minor League”?  Which does it actually mean, majors or minor leagues?

Confused Diamond Girl