From scratching around in Google I think the heraldic chevrons, point up, lower sleeve may turn out to show which "entry"/ seniority year the entrant was in.
False alarm for Good Conduct badges ........ in the good old days the RAF had the same system as the RN, up to three badges, carrying extra pay, and taking a good few years to accumulate. Although the army had a similar system dating back to 1836 or so, and men could have incredible numbers of badges, the extra pay was phased out in the years before the Great War.