New Brevoort Formspring

Tom, has Ms. Marvel's "S" on the chest ever been explained / referenced to something? I tried looking it up, but I couldn't really find anything. The only thing I found is her admiring the Sentry in the past and that she started off as the "Sentress" with a Sentry like costume, but Sentry came out AFTER Ms. Marvel?! It's so confusing!