SpamAssassin Rule: URIBL_RED
Standard description: Contains an URL listed in the URIBL redlist
From the about page.
"red.uribl.com - This list contains domains that are not listed on black and are either very young (domain age via whois), or use whois privacy features to protect their identity. This list is automated in nature, so please use at your own risk."
The default scores for this rule can be found in the online list of tests.