Sometimes a SKU, a barcode, sometimes a manufacturing date, often just the product code and quantity (TR30, RT20).
Never the full name of the molecule. That way, they can always deny what it is.
Never a batch number, so as not to make it too easy to identify the factory. Partly because this sale is illegal everywhere (and they’re in China, where execution as a public example still exists), and possibly because some factories might be official subcontractors for major pharmaceutical companies.