"Ping Token" is what Blip Tokens were called in the prototype version of Chronicle X. At a few places, that term has survived on cards and rules.
Blip Token
Blip Tokens are the form the Alien Forces initially take when they are deployed on the Mission Map. The represent a "radar echo", and are marked by facedown tokens with the downfacing side showing which Alien Type it is. The Alien Forces also gets two Decoy Tokens each Mission, which are small drones without combat ability.
Whenever a Blip Token enters into a Hero's Line of Sight, the Blip Token is flipped over, and the corresponding Alien Type Model or Models are placed on the Mission Map. When a Decoy Token is flipped over, it is taken off the map, and no Model is placed.
A Blip Token is also flipped over and revealed if anything in the game would cause damage to it, or needs to know any of its stats other than Movement. The Movement stat for a Blip Token is 5, no matter what type of Alien Unit it actually is.
The Alien Forces can also explicitly flip over and reveal one of their Blip Tokens as an Action when activating it.
When a Blip Token is revealed either due to the actions of the Hero Players, or by the actions of the Overmind Player if the revealed Alien Unit is in Shoot attack range of a Hero, it triggers an Alien Behaviour action. (This point is confusingly described in the rulebook, and confusingly clarified in the FAQ...)
If the Blip Token was revealed because something was about to cause damage to it, apply the damage to the revealed Alien Unit instead.