**disclaimer, not a zta***
the zta's on my campus had really nice quarter zip pullovers made for their mothers with "ZTA" on one line above the left breast and "MOM" right below. I loved it so much, I had one for my mother made exactly like it!
The best person to answer your ? is an older girl in your chapter for sure though!
Also, plenty of National HQ boutiques make lettered apparel for parents, ill check on the zta site and see for you! If your NHQ is selling it, it is obviously 100% appropriate
ETA:
here you go! one of these zta mom tees is a safe bet
Threaded Mode
