Future Hiro's message
The Message is
Save the Cheerleader, Save the World.
About
Collision
Future Hiro travels back in time and tells Peter Petrelli the message. Future Hiro asks Peter to pass it on to the present version of Hiro Nakamura when he calls. Peter receives Hiro's call at Isaac's studio, and tells Ando (who translates for Hiro) about his encounter with Future Hiro. Peter delivers the message to Present Hiro, as promised.
Hiros
Peter is convinced that one of Isaac's paintings holds the key to the puzzle. Before they can "save the cheerleader", they must first find her. Peter feels the missing painting from Isaac's set is the key.
Fallout
Hiro and Ando discuss the message at Union Wells High School after its Homecoming disaster. Ando suggests that the message is actually two separate statements, "Save the cheerleader", then "save the world." Hiro states that the message is an "if-then" statment, not two separate statements.
Fan Theories
Please refer to Theory:Future Hiro's message for fan-created theories and other speculation.