As a researcher and writer on military club tokens (and chips), I can be very helpful with identifying these chips. First, the facts:

Rocker 4 refers to a rank, usually (but not always this would refer to the top four enlisted ranks of a military organization.

APO 500 was in use between August 1942 through Dec 31 1957 for a number of locations, including among others, Australia, the Philippines, and Japan, with the longest span of time and the most locations, Japan.

If you know the date that the chips were mailed, I can give you an exact location and possibly even the name of the base that they were used at!.

I am in the process of working on cataloging military chips (along with California Card rooms, and Wet chips among others). Am also starting on a new project for North Dakota Charitiy chips.

Always gald to help. Thanks for the scans and the APO #, helps out a lot!

John