Which type of material/stationery/signage must a company's ACN be shown on?
A company's ACN must be shown on company documents to ensure identification of the company when transacting business.
The ACN should appear on all of of the company’s 'public documents' and 'eligible negotiable instruments'. These include all documents that are lodged with ASIC, orders for goods and services, business letterheads, cheques, and written advertisements making a specific offer capable of being accepted.
The ACN should be clear, easily readable and obvious as to the company to which it relates.
Where the ACN is not required
There are certain items where the ACN is not required, including packages and labels (including envelopes), advertisements that don't make a specific offer capable of acceptance (such as advertisements that promote the company and its goods and services in general), credit cards and vouchers, cash-register receipts, business cards and 'with compliments' slips.
ASIC provides more information on their website.