That is not a "disqualification code". It is a draft board filing number. For some reason the Pulaski County Draft code stamped the number in the space left for the filer to write in their "physical" disabilities that would disqualify them from service, ie: loss of a limb, eye, lame, paralysis, etc. If you look at cards for others you will see the same type bold number+letter stamped at top of front or back of card or other places.
He probably didn't serve because of his age and it was the "last" registration...Sept 1918 and Armistice (end of war) was November 11, 1918.
Even Ancestry has the statement in explanation of the cards that reads "only a small percentage of these men who registered were actually called up for military service."
Since I see a faint check mark on first blank line after question, I take that to mean he saw the question and had nothing to write.