One of Sigil's Factions, the Believers of the Source hold the popular belief that all beings are capable of ascending towards Godhood. Life is a series of tests and trials, say the Godsmen, and each death brings you up (or down) to the next trial in the eternal Ladder of Being, the top of which is Godhood itself.
In Sigil, the Believers make their headquarters in the Great Foundry, where all of Sigil's metalwork is done. From horseshoes to cooking pots, to nails and rivets, to simple eating utensils, any common item made of steel likely comes from the Foundry's forges.
Faction Benefits and Drawbacks
The philosophy of the Godsmen is extremely inclusive. The fact that they believe everybody has the potential for Godhood, combined with the belief that physical forms are just shells carrying the spirit from one trial to the next makes them a very open-minded and tolerant bunch. This makes them very welcome across the Planes, and normal NPCs Reaction to Godsmen PCs is always one higher than it would normally be (Indifferent to Friendly, Friendly to Helpful, Unfriendly to Indifferent, etc). Naturally, this does not apply to the Faction enemies of the Godsmen, particularly the Dustmen, nor does it apply to NPCs who have other reasons to be hostile to the PCs question. As always, DM fiat applies.
Godsmen believe in reincarnation as a natural part of the Ladder of Being. Any Godsman PC who dies during the game can opt to return to the game in a different physical form, as per the Reincarnation spell. The exact physical form is up the DM, and does not necessarily have to come from the list provided in the Reincarnation spell description.
Lastly, Clerics and other classes that draw power directly from a Deity suffer from a lack of faith in their deity (given that anybody can ascend to Godhood, they can't be THAT special). This translates into a -1 penalty on all saving throws.