OID value: 2.16.840.1.113730.1.2
The value is an IA5String. When present this string is added to the beginning of all relative URLs in the certificate. This extension can be considered an optimization to reduce the size of the URL extensions.
URL for further info: http://www.netscape.com/eng/security/cert-exts.html
See also the OID Repository website reference for 2.16.840.1.113730.1.2