Every costume category in the 501st Legion has different levels of accuracy. Stormtrooper costumes have three: Basic approval, Expert Infantry and Centurion.
The First Imperial Stormtrooper Detachment finally got to approve the 1000th Expert Infantry costume a couple of months ago after doing a “March to 1000” campaign the past year.
To mark the occation, every eligible* troopers could get one of these pins:
My pin arrived today. I got approved at the Expert Infantry level on October 30, 2017, and I was number 767.
If you want to learn the difference between each levels, see the CRL: https://databank.501st.com/databank/Costuming:TK_anh_stunt
*) Have one of the first 1000 approved Expert Infantry costumes.