Travis hates the filth of New York City in the summer, and he wishes for a great rain to wash it all away. His definition of filth includes not only the smell of the city or the garbage, but also the people who live in the city, including the black people in Harlem and the prostitutes and hippies in Times Square. In one of his first diary entries, Travis expresses gratitude for a rain that has left the city slightly cleaner than before, but he adds that someday a "real" rain will fall to clean up the city. By this Travis is imagining an apocalyptic flood, one that will separate the people he thinks should be redeemed from those who are not worthy or clean enough. Water takes on the qualities of a redemptive, baptizing force when Travis gives a ride to a prostitute and a john and goes out of his way to drive his cab through an open fire hydrant. He bathes the exterior and interior of his car, both of which have been corrupted by the passengers.
A common lesson for young screenwriters is that a gun that appears in the first scene of a movie must go off before the credits roll. Taxi Driver mocks this axiom by giving its hero, Travis, four guns and a knife. The film is full of guns. Travis views them with a certain reverence, and the first and last shots of the .44 Magnum are slow close-ups panning from the handle to the barrel. Guns take on a powerful significance in Travis's emotional life. He buys his guns only after having been rejected by Betsy, and in a way they help him to be potent after his failure at courting her.
Fake guns have significance as well. Travis and other male characters frequently use hand motions to simulate shooting. The hand has the power to insult and offend, but no power to do any physical harm. Charlie T is the first person to make this hand gesture at Travis, accompanied by a verbal shooting noise, even before Travis buys his guns. Later, Sport makes the same motion when Travis visits Iris. These men mock Travis when they pretend to shoot him, and he is put off by their gestures. After the final shootout, when Travis has no bullets left and the police arrive, Travis puts his hand to his head and pretends to shoot himself. In his maniacal state, he seems to believe this gesture will actually work.
The $20 Bill
When Travis first encounters Iris, she enters his cab and is pulled out by Sport, who tosses Travis a $20 bill to keep him quiet. Travis takes the money, but he leaves it on the front seat, separate from the rest of his cash. Subsequently, whenever Travis sees the folded bill, he remembers Iris, the filth of the city, and his own silence. For Travis, the bill symbolizes the city's corruption, where anyone can be bought, like a prostitute, for the right price. The money serves as a constant reminder of his own complicity in Iris's situation, and it eventually spurs him to action. He is ashamed that he took the money in the first place, and his shame motivates his later actions. When Travis visits Iris in her room, he uses this bill to pay for his time with her. He returns the money to the man it came from in an attempt to atone for his previous inaction, the first step in his new role as Iris's liberator.