At the time ZSSD had both Mandarin and Indochinese Sika. (They also had MacNeill's Red Deer which I was hoping you'd have a photo of), It could be either one, I'm leaning towards Indochinese myself, but that's not based on anything in particular.
I'd have to check on MacNeill's Red Deer photos...unfortunately as a general rule I used to not worry about subspecies when I was photographing, especially since I had to pay for film and developing so I was stingy with extra pictures. Of course this cost me from taking any pictures of the Bush Pigs they had on exhibit because at the time they shared species status with Red River Hogs.
You know what, I take that back. Ituri corrected me, the WAP had Formosan. As the Indochinese is Cervus pseudaxis it would make sense since this looks like a false Axis.
Also I checked on the MacNeill's Red Deer, and it doesn't look like I have any photos of those. I have Bactrian Deer, Barbary Red Deer, and Altai Wapiti at different times at either the Zoo or WAP.
Any clue what years the MacNeill's Red Deer were kept at the zoo. I didn't go to the Zoo between 2002 and 2010 (and thus never got to say goodbye to Horn and Hoof Mesa!)