There is no such thing as a commercial Lithgowicon. The original butt will have the rifles history stamped on it. The date will be on the barrel with a bundle of inspectors and proof marks unless it is a civvie replacement. The serial number on the barrel may have another Number immediately above it and there could be a single didgit number on the Knox flat something like 2MD.
The police in some states were issued Lithgows and will have stamps indicating ownership but will have the Lithgow marks the same as all other Lithgows.