I think for this to be useful and assuming people wanted this then dang may have to first block VPN's and then country would have to be learned after 99%+ of VPN's are gone as many accounts could have been created using a VPN.

If not blocking VPN's, then display "Possible VPN".

Perhaps to get some adoption, make it opt-in and also let users enable flag-display at the risk of giving off 4chan vibes.