Signature is related to Mark. Mark is a synonym of Notice. Notice is related to Invitation. 
you would Communicate because Cooperate. Cooperate is etymologically related to Operate. Fly is a type of Operate. 
Signature <--RelatedTo--> Mark <--Synonym--> Notice <--RelatedTo--> Invitation 
Communicate --MotivatedByGoal--> Cooperate --EtymologicallyRelatedTo--> Operate <--IsA-- Fly 