Can any one tell you what the On the front Long Service AAOCL badge represents?

AAOCL stands for Anglo-American Oil Company Ltd. My great uncle was awarded one of these long service badges. A yellow-metal lapel stud badge in the form of a six-point star with a small diamond at the top. It is inscribed on the back with his name and 'May 1928', the year that he joined the company.