@adz
It was a Chinese prison, though it was IIRC commandeered by the Japanese. I don't really know anything about Chinese or Japanese orthography, but having looked at some symbols from both it just looked more similar to the Chinese system to my untrained eye. The Japanese symbols seemed to be less geometric than the Chinese, with more curved lines. But then, if I understand correctly there are several forms of orthography in both Chinese and Japanese depending on the region/dialect, which probably confuses things further.
As for the symbol representing the number, I'm not sure. I did wonder about this, and looked in to both the Chinese and Japanese numerical systems. They both seem to construct larger numbers by combining multiple symbols, rather than having the whole number collapsed in to one symbol. (Similar, I suppose, to arabic numerals).
The dog tag belonged to my other half's step dad's father. All we know is that he was held in Changi by the Japanese for three years during WW2. Unfortunately, we don't have any more information.
Apologies for my ignorance, and for any glaring errors or assumptions in my interpretation of Chinese and Japanese language ;-)
