Bronwyn
Below are the cap badges of both the Cameronians (left) and the HLI cap badges.
The Cameronians (Scottish Rifles) had a Mullet, over a stringed bugle, surrounded by thistles. It was a large cap badge and was very distinctive. Additionally, you would expect to see black buttons on a rifle regiment.
The HLI, had a small cap badge similar in style to the Royal Scots.