No, We're Pretty Sure This Sound and Fury Is Signifying Something
First things first: these are the lines from Macbeth we hear in the film:
The queen, my lord, is dead.
She should have died hereafter;
There would have been a time for such a word.
To-morrow, and to-morrow, and to-morrow,
Creeps in this petty pace from day to day
To the last syllable of recorded time,
And all our yesterdays have lighted fools
The way to dusty death. Out, out, brief candle!
Life's but a walking shadow, a poor player
That struts and frets his hour upon the stage
And then is heard no more: it is a tale
Told by an idiot, full of sound and fury,
The italicized lines are recited, not by a trained Shakespearean actor, but by crazy street person. This dude's belting these lines out at the top of his lungs as Riggan walks in a daze through the New York City streets at night.
And yes, these lines inspired one of the great novels of the 20th century and we could unpack them for, quite literally, pages and pages…but let's ask how they relate to this specific moment in Birdman when Riggan is essentially at rock bottom.
"To-morrow, and to-morrow, and to-morrow" cries the man, almost in despair. This isn't a happy song about how the sun always rises. This ain't a production of Annie. These tomorrows speak of a painful infinity that slowly drags out, just like the recitation itself. There is a futility in living but also in dying, as Riggan learns after his failed suicides.
He feels small and powerless and alone…and feeling small and powerless and unknown is exactly what Riggan fears most. He's terrified that he'll "strut and fret" his "hour upon the stage" and then will be "no more." He'll simply be the next dead celebrity, filling Instagrams around the world for a few days until memory of him fades away, the next Farrah Fawcett unable to measure up to the Michael Jacksons of the world.
Of course, Riggan is the idiot telling the tale that's full of "sound and fury, signifying nothing." This tale is the Birdman franchise in a nutshell: a franchise filled with meaningless action, explosions, glamor and all the big flashing lights of celebrity and money and fame—basically everything that Tabitha hates and everything that makes Hollywood Hollywood.
These lines also pertain to his play: Riggan's also worried that he's turned Raymond Carver's story into a senseless play that no one will understand or care about. And, of course, they're also about his life, filled with the sound and fury of all these movies and plays and relationships, all of it meaningless as it roars together in Riggan's head.
Bleak? Oh yeah. A little dramatic? Also: yes. But symbolically meaningful? A resounding yes.