Thank you everyone! This is all good information. The date of 1887 would make him 18 years old, which matches his appearance.
I have attached the requested high-res scan of the shield, but I could make nothing out on it.
I have also attached another scan of the two prints of the same photo. The one on the left is about 5x7 inch, the other is about 2x4. I was interested that it is on two different card mounts, one from Belfast and one from Limmerik. The back scanned above is the right hand photo. The back of the other is dark grey and blank.
I also have another photo of this fellow's children, from the same Belfast studio, taken about 1908 I think (based on the ages of the children.
The story is that while serving in Ireland, he met an Irish girl, who he took home to Scotland and married. They lived in Edinburgh, but the wife and children spent six weeks every year in Ireland. Luckily, someone in the family was very photo-oriented, so we have a good spread of photos of William right through to old age.
