Any numbers relate to the type of clay being used (often a test). In this case, the body is Plainsman P300. The fluted foot ring (for better draining in the dishwasher) is also a tell-tale sign the mug might be made by Tony.
Tony Hansen is the author of Digitalfire Insight, Digitalfire Reference Library and Insight-Live.com, he is a long-time potter, ceramic lab-technician and body and glaze developer.
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