Last month of winter in Ancardia.
Death, Messengers, Companion, Tricks
Harder to trick by deceptions, messengers will reach you faster, you are faster (+10 to speed), companions are more powerful, +2 to initial Perception.
1. "Harder to trick by deceptions" is partial resistance to doppelganger confusion attacks. About 1/3-1/4 of "doppelganger suddenly looks like you" attacks are resisted. Whether it has any effect on other attacks [like stun from the Arena master] is unknown at the moment.
For itself it is a rather weak effect, except for characters heavily relying on missiles or when running in tension rooms of doppelgangers early on.
2. "Messengers will reach you faster" Delivery of the rune-covered trident happens faster, at level 16 rather than 36. This is one of its best effects; the Trident deals good damage and is a demon slayer, and unless the PC was lucky at pre-crowning or crowning this will almost certainly represent a significant upgrade for the melee weapon. Since the Ancient Chaos Wyrm happens to be a demon, this means Raven born characters get a guaranteed way to kill him, just in time before the tower. For characters relying on melee this is rather strong.
3. +2 perception. While perception probably has some minor effect in trap avoidance and hearing some sounds, for line of sight considerations breakpoints in the early game [each adding a tile of line of sight] are 5, 10 and 20. So while it might be useful for something like an orcish archer, most characters won't notice a significant difference [with or without it, most characters are between 10 and 20 points anyway].
4. "you are faster (+10 to speed)" - best known effect of the month which is better than all three speed talents combined... Speed is hard to beat and undoubtedly useful for all characters. The only downside is xp penalty [basically the character gets 9% less experience]. Well, this can in general be counteracted by burden levels and satiation, but xp is a serious issue for trolls. Some classes [like mindcrafters and in a minor way all characters involved in spellcasting due to some spells scaling to level] might also think of this as not so advantageous.
Overall very strong effect for melee and missile oriented characters, value for spellcasters depends on playstyle.
5. "Companions are more powerful". While this is considered to be a bonus to Bards, this is not exactly true.
This sign does not influence the strength of starting companions, slaves generated by necromancy, stats your pet gains from leveling, or tamed animals.
Sign does influence strength of companions gained by reading scrolls of familiar summoning [probably adds DL upon creating one]. Since most characters have easy access to the bug temple [surface level] and dwarven halls, both of which have very high DL, this effect is close to non-existent.
Very good sign for any melee or missile oriented character. Less impressive for spellcasters. Despite popular belief does not give any particular bonus to Bards. Not advised for trolls.