Secret Agents (commonly called "SA's") is an elaborate espionage game invented by Jordan Pike and popular among the Pike kids and their friends. It involves "agents" performing assigned tasks and being rewarded with color-coded badges representing successively higher ranks.
SA's is first seen in #13, when the Pike kids dedicate themselves to spying on their weird new neighbors, whom they believe to be foreign spies. Vanessa earns a yellow badge for looking in the Congdon's window; Nicky earns a green badge for setting up a tape recorder in a nearby tree. Claire and Margo earn white badges for ringing the Congdons' front doorbell and hiding. Vanessa earns a green badge for using binoculars to peer into an open basement window.
Ranks of badges
From lowest to highest: