Life-sign signature
From The Stargate Omnipedia
The digitized state of life forms while they are held inside a Wraith Dart's culling beam memory buffer. Readings appear as simple blips, with no way way of identifying one individual from another.
KEY EPISODE
Duet - Colonel Sheppard is eager to extract Dr. McKay from a Wraith Dart in order for him to get out Lieutenant Cadman as well, but he is forced to pick one of the blips on the screen, not knowing which is which.