Agent Garrett says that he isn't a true believer. Stan Lee often referred to Marvel fans as "true believers."
After the team decoded the Hydra signal, Coulson quotes the Hydra Oath "Cut off one head, and two more shall take its place." Garrett reacts confused and ask if it wasn't a limb. This is a reference to the comics, where the Hydra's oath is: "Hail, Hydra! Immortal Hydra! We shall never be destroyed! Cut off a limb and two more shall take its place! We serve none but the Master--as the world shall soon serve us! Hail Hydra!"
"Turn, Turn, Turn" originally aired on ABC on April 8, 2014, and according to Nielsen Media Research, was watched by 5.37 million viewers.