You never had any Premium time on this account before, right?
I ask that because I am with my main as a Free Account character, but since he had premium time in the past this icon isn't showing up.
However, I compared it to another account that never had any premium on it, and it indeed shows up right where you are showing. Unfortunately, you will only get rid of it after the first acquisition of premium time (but it will never appear again, as far as I know).
EDIT: I still need to test if buying something on store may remove this thing... However I will only be available to test it in the future.