Hey deino, I apologize in advance for my lack of information on whether the tailart is actually painted on or a watermark, but there seems to be a few other things on this J-16 that stand out.
Firstly the lack of a serial number, but I believe you noticed that... Secondly, according to the image there doesn't seem to be a second pilot nor his/her ejection seat. Thirdly, this paticular J-16 seem to have 2 new antennas: one on the back just in front of the airbrake, the other one on the underside of the head, with both painted yellow. I have no information on the one on the back (afiak no other Chinese flankers have an antenna of this size or shape at that place) but the one on the head seem to be identical with what the J-11D prototype has (credit to my friend who noticed this)
Hmmm ... indeed strange!