A company seal is a rubber stamp with the company’s name and Australian Company Number or ACN. It is the same thing as a common seal or a corporate seal.
Prior to 1988, company seals were mandatory for the execution of documents and it was compulsory that a seal was affixed to deeds. The Company Law Review Act 1988 abolished both requirements.
Regardless of the law, many companies today still choose to use a company seal. For instance, a company seal may give more legitimacy to documents for people unfamiliar with the Australian way of document execution. If a company has many overseas clients, this may be a way to show legality and validity.