"The Label Code (LC) was introduced in 1977 by the IFPI (International Federation of Phonogram and Videogram Industries) in order to unmistakably identify the different record labels (see Introduction, Record labels) for rights purposes. The Label Code consists historically of 4 figures, presently being extended to 5 figures, preceded by LC and a dash (e.g. LC-0193 = Electrola; LC-0233 = His Master's Voice). Note that the number of countries using the LC is limited, and that the code given on the item is not always accurate." http://www.iasa-web.org/icat/08_0.htm
When entering a Label Code in MusicBrainz, use only the numerical part, with or without leading zeros, which is the only relevant part stored in the database.
Note that subsidiaries do not necessarily have an independent LabelCode, and may just use the LabelCode of their parent label.