From the sound of it, John Herson is just as mystified how this got missed as you probably are. There are no Master Game symbols on the 2012 baseball XC set.
For those who want them, you can download them from the APBA website. They are in pdf form. Here is a link to the XC MG symbols and you can find the lineup sheet of the XCs here.
Got my 2012 xc’s today and noticed no master symbols on the cards.
I went to apba’s web site and it says beginning in 2011 the symbols would be downloadable only.