You will see the miles show up in your account every month. Other than indirect evidence like that, or calling CO to verify, I don't think there is any "flag" or anything else on CO.com that verifies you are a PP cardholder.
I don't think the "Flexible Elite Miles" appears until you get your first 2000 miles.
I am positive it will show once its linked even if you have not earned any flex eqm.