Montag does have a helmet with 451 emblazoned on it, the temperature at which paper burns, a symbol that firemen have been turned into censors, burning books. But he also wears two other symbols on his uniform: a salamander on his arm and a phoenix in a disc on his chest. The salamander is a fitting image for a fireman, for salamanders were once thought to live in fire and thus to have the ability to withstand its flames. The firemen that burn the books likewise are supposed to have the ability to withstand flames. The phoenix is a mythical bird that when burned arises young and reborn from the flames.
The salamander also has a more ironic meaning in the novel. First, as Faber points out, the "salamander devours his tail," meaning in this case that the underground is starting to use fire against the firemen by burning firehouses and firemen's residences. The firemen's weapon is becoming the source of their destruction. Second, Beatty, the fire chief and figure in the novel who most represents the world of book burning, is destroyed by fire.
Bradbury also shows that the phoenix has been appropriated by the very men, the renegade book readers, whose books the firefighters are out to destroy. Near the end of the novel, Granger speaks, and the phoenix becomes a cautionary symbol of the past while the broader and more hopeful context of the underground movement becomes the real site of rebirth:
There was a silly damn bird called a Phoenix back before Christ: every few hundred years he built a pyre and burned himself up. He must have been first cousin to Man. But every time he burnt himself up he sprang out of the ashes, he got himself born all over again. And it looks like we're doing the same thing, over and over, but we've got one damn thing the Phoenix never had. We know the damn silly thing we just did. We know all the damn silly things we've done for a thousand years, and as long as we know that and always have it around where we can see it, some day we'll stop making the goddam funeral pyres and jumping into the middle of them.
Montags helmet has the number 451 on it. This alludes to the title of the book "Fahrenheit 451" and happens to be the temperature at which paper burns. This is an obvious reflection of the fireman's job in the novel, which is to burn books. Montag also wears a picture of a salamander on his uniform. The salamander is a mythical lizard who can live in fire. This is a symbol for the destructive forces for which Montag and his company use fire.