Code 9
From The Stargate Omnipedia
S.G.C. alert, typically used when a member or members of base personnel have been compromised or abducted.
KEY EPISODES
Spirits - O'Neill uses a Code 9 when he fears SG-11 has been duplicated by aliens.
Fair Game - When O'Neill is snatched from the S.G.C. by the Asgard General Hammond issues a Code 9.