Boot page flag for cleanly shut down database
It's part of the dbi_status field, which as Sean Gallardy said aren't documented and no-one's blogged about them (yet - so I don't want to get into details here). You can experiment with open transactions, crashing the server and moving the log file to force a database into the RECOVERY_PENDING state to watch which bits get set (again, no blog post about that yet).