ISO 4031 is an international standard first issued in 1978 by the International Organization for Standardization. It defined the representation of local time differentials, commonly referred to as time zones. It has since been superseded by a newer standard, ISO 8601. This newer standard sets out the current formats for local time differentials and so ISO 4031 is no longer in use.
References
ISO 4031 Wikipedia(Text) CC BY-SA