You see with the birds working for the bourgeoisie they are in disguise as these normal birds to typical humans hence the name Spies in Disguise. This is because Will Smith Character, the spy, gets transformed into a bird and birds are in disguise essentially acting like spies for the bourgeoisie, the social class that came to own the means of production during modern industrialization and whose societal concerns are the value of property and the preservation of capital to ensure the perpetuation of their economic supremacy in society. Because birds exist within the sky, the movie, Spies in Disguise, intentionally sounds like Spies in the Skies.