ACN
Under the Corporations Act 2001, every company in Australia is issued with a unique, nine-digit number, an Australian Company Number (ACN). Companies are required to disclose their ACN on: the common seal (if any) and every other seal of the company (if any); every public document issued, signed or published by, or on behalf of, the company; every eligible negotiable instrument issued, signed or published by, or on behalf of, the company; and all documents required to be lodged with ASIC.
An ACN is not required on (at least): packaging and labelling, including envelopes and transport documents; advertisements which do not make a specific offer which is capable of being accepted (such as advertisements which only promote the company and its goods or services in general); credit cards and credit card vouchers; machine-generated receipts, including cash-register receipts; business cards and 'with compliments' slips; and items which are not documents (e.g., vehicles, television advertisements).
An ACN remains unchanged even if a company has a name change or is deregistered.
Read more about this topic: Australian Company Number