Serial Item and Contribution Identifier
The Serial Item and Contribution Identifier (SICI) was a code (ANSI/NISO standard Z39.56-1996 [R2002]) used to uniquely identify specific volumes, articles or other identifiable parts of a serial. It was "intended primarily for use by those members of the bibliographic community involved in the use or management of serial titles and their contributions".
Source: Wikipedia — Serial Item and Contribution Identifier (CC BY-SA 4.0)