Did POW issue a certificate? I thought they were just sold with provenance (the back and forth email exchange between Banksy and the dad)?
Edit: There is a chance that I dreamt that though.
I'd be very surprised if they did. I asked the auction house before if there was a COA and never received an answer so I didn't pursue further. Odds are that if it had a COA it would have been at a more prominent auction house and similarly the result would have been exponentially higher. Given the circumstances, I'd be shocked if it had one. Still, a pretty cool looking piece.