The Ten Commandments
As he explains in Chapter 1, Paine believes the Ten Commandments to be a perfect example, and thus a symbol, of doctrine accepted as fact without any real evidence to support this acceptance. God supposedly gave Moses these Ten Commandments on two stone tablets on top of a mountain, and, as Paine says, these commandments are no better than those of any given lawmaker. The assertion that God himself gave Moses these laws is no better than hearsay, and it is thus not to be believed.
Galileo
Galileo was a Florentine astronomer and mathematician who was persecuted for his counter-ecclesiastical theory that argued from reason and objective fact that the Earth orbits the Sun, and not the other way around, as had been traditionally accepted by the Church. Paine uses Galileo as a symbol for all the brave men (including himself) who have stood up and will stand up against the tyranny of the Church in order to bring truth to the world.
Jesus Christ
In this book, Paine argues that Jesus, while a verifiable historical figure, never made any claims to Godhood, and that these claims were later forced upon him by other writers. This is a symbolic example of his description of the establishment of unprovable hearsay as dogma; Jesus Christ, now the primary figure in "Christ"-ianity, is no longer a symbol for salvation, but a symbol for manipulation.
The Church
Paine uses the Church itself as a symbol. He believes that the best society is a free one, so he undertakes the noble mission to free society from its constraints. The worst tyranny of all, he says, is that of religion, so in The Age of Reason, he argues that the Church is a terrible tyrant that must be dealt with. The Church is a symbol of manipulation and establishment of "truth" based on nothing more than hearsay; it is therefore the symbol of everything he's fighting against in this book.
The Age of Reason
Paine even views this work itself as a symbol. It represents the efforts of brave men like himself and Galileo to bring hard truths to the brainwashed peoples of the world. This book, actually published in a series of pamphlets, is a perfect example of such a work; it purports to free its readers from the captivity of tyranny in order to make society a more rational and therefore more honest place.