FSU, I know there's nothing official about wearing letters, it was definitely a chapter thing, and I stress again it was a pledge class vote. Alpha Phi class (my class) just chose to go with tradition was all. We had plenty of other Zeta stuff to wear, just not the stitched letters. We got tons of shirts from our Crown, Strawberry, and Bunny sisters before we got our big and then our big gave us stuff too.
And my family tradition was to give our family letters to sisters at initiation, along with the crest afghan (something I started, my big gave me chapter letters which they later changed the colors of, but oh well).