R is for Railroads because when Montag escapes the Hound he hides by the railroad tracks. When he hides there he meets Granger and his group of friends who help preserve books. Montag is helped and accepted by Granger's group of scholars.
S is for society because in Montag's world they live in an dystopian society. In this world the residents try not to think too much. They like life in the sense that they can get whatever they like whenever they like. They want to be able to fill their wildest desires in a heartbeat.
T is for Time because when Montag is fleeing the Hound he needs time. Montag wants to have more time in his life rather than dying. He wants to have time to learn to comprehend, understand, and enjoy books.
U is for Umbrella because when Montag finds Granger and his friends they accept him and provide an umbrella of support for him. Granger takes Montag under his wing and guides him through their new lifestyle. Montag is protected and cared for in his newfound group of friends.
V is for Virtues because when Montag is living in the city they don't have a lot of virtues. The citizens don't have any realization of normal life. They believe that they can get anything they want in an instant. In their dystopian world this might ring true but in the real world it's not.
W is for Watching because Granger and his band of buddies watch over and protect Montag like they would protect another one of their friends. They can teach Montag how to understand things and he gets a better perspective on life. They travel the country helping people remember what the world was Ike before the war.
X marks the spot because when the missile hit the city it hit its mark. I will assume the X marked the spot and that spot was the city. The city was crushed and nothing was able to survive the attack.
Y is for Young because when Montag finds Granger and his friends he gets a new start. In that new start I'd guess he feels young again. He gets to restart his life with these friends and he gets a second chance.
Z is for Zero because when the city got hit by the nuclear missile it was reduced to zero. Nothing survived in the city and no one lived in it again. Montag was outside it with Granger so he survived as did Faber who was on a train to St. Louis.