Is the Project Tracker artifact code unique?

Any number of projects can use the default artifact code 'SC'. User defined codes must be unique for every project. However, subprojects can use the artifact code of their parent project. NOTE: Subprojects do not inherit the artifact code of the parent project by default. If the project owner wishes to use the parent project artifact code, (s)he must specify the artifact code of the parent project during sub project creation.