The names on the board could provide a clue as to the year when this photograph and the others in this gallery were taken.
On the original image the notice board reads
17/21 Lancers
18 Field Ambulance
216 Ghurka (this line is VERY faint, but this might be correct)
SIG SQN
Comments
17th and 21st Lancers
Some information here on posting to Hong Kong.