* use the !squirrel stalk word in #releng
* Follow the escalation route at https://wiki.mozilla.org/ReleaseEngineering#Contacting_Release_Engineering
* ping in #taskcluster (see https://wiki.mozilla.org/TaskCluster for coverage in any timezone)
Other signs of a global issue include:
* you see nagios alerts for the issue in #sysadmins
* there's already a whistle pig notification (https://whistlepig.mozilla.org/) (but still let MOC know it's tree impacting)