This warhammer is made from good materials (it is Quality +2), and has four deep red gems set into it. In a darkened place, you may notice that the gems have small glows inside them like nearly-cold embers.

Possibilities:

1. In battle, the gems glow more brightly; once the weapon has tasted blood, the gems appear to burst into fire.
2. When the warhammer is used in anger — that is, when you have an enemy named in one of your Traits and it brings you to strike at them, or when you are striking to fulfill a vengeful oath — it will strike especially hard, with a blunt damage factor of 14.
3. If used to strike a door or other wooden structure, the warhammer will burst into flame and knock the structure into smithereens.
4. What appear to be gems are actually rock crystal domes; the interior of the warhammer courses with blood. It pulses even faster when in battle.
5. When properly invoked, each of the four gems can summon a fire elemental of significant potency. However, each elemental will seek to destroy the warhammer itself if given the chance.
6. When the warhammer is held aloft and you make a proper speech, all troops on your side will be filled with camaraderie and determination to win in battle. In game terms, your side gains +2 in morale.
7. When the warhammer intercepts another weapon in combat, both will erupt into fire and, if the opposing weapon is made of wood, it will catch on fire.
8. When the bearer is grievously injured in combat, one of the gems will go pale and the bearer will suddenly feel refreshed. In game terms, this means when one of your characteristics is reduced to 0, one of the gems will go pale and the characteristic will be returned to its normal level. Once all four gems have gone pale, it will no longer work for you.
9. The warhammer was forged in Chakotha, shortly before the Great Conflagration there. As such, the weapon was witness to the horrors that occurred. The gems were originally pale green, but as they saw more bloodshed, they grew redder and redder. The last owner was the last of the native defenders of Chakotha to fall. If you ask in the right language, the warhammer will convey the full horror of the Conflagration, and make clear to you that it wishes never to see war again; if allowed to not see combat for a full century, the gems will return to their pale green state. However, this is unlikely to happen, because the weapon is also highly effective in battle (Quality +4).
10. The warhammer feeds on anger. Each time you use it to strike a target in anger, one of the gems will begin to glow brightly and you will slowly become an angrier person. In game terms, whatever your highest Trait is, it will shift (over a course of four stages, with intervening stages as decided by the GM) to become Angry.
11. The warhammer can double as a smithing hammer, in which use it excels; the gems will soak in the heat of the smithing fire and allow you to smith far longer without returning the item to the fire, adding +2 to any smithing attempts.
12. Whatever other effects it has, they are even stronger when the warhammer is carried by a woman at the time of the full moon.