A Week Full of Daggers: Delver's Dagger

Fantasy roleplaying has always had a lot of very memorable magical weapons, but the vast majority of them are swords, axes, hammers, and similar big, nasty implements of destruction.  Magical daggers generally haven't gotten anywhere near as much love and aren't nearly as well-remembered as, say, a +1 Flame Tongue sword, or a Hammer +3, Dwarven Thrower, or a +2 Nine lives Stealer blade.  Magic daggers often wind up as a backup weapon that rarely sees use, or a nearly-forgotten last resort for an exhausted wizard.  Even stabby roguish types tend to prefer short swords to daggers for mechanical reasons in many systems.

So, I'm taking the next week to put up some ideas for knives, poniards, daggers, stilettos, and other breeds of small blades that your players might actually remember rather than stick on their inventory sheet and forget until they need something to distract a rust monster or spike a door.  They'll be system-agnostic, with some suggestions on "D&D-ish" mechanics where called for.  Mostly I expect folks to be able to hack their own rules to suit their pet system, though.

Without further ado, I present today's entry:

Delver's Dagger

Description:  A well-made but unremarkable dagger, with a blade about 7" long and a sturdy cross-guard.  The pommel is a disk inscribed with a stylized sun on one side and a moon on the other.  Magical senses will reveal an aura of power that suits the potency your campaign needs, as these blades come in many levels of power.  The dagger's light-shedding power (see below) fails to register even under strong magic, although it may detect a suggestion of some concealed ability.

Powers:  In addition to the usual combat enhancements found on an enchanted weapon, the blade sheds a 30' radius of dim light when drawn.  This light sheds no shadows and can only be perceived by creatures whose blood (or corresponding internal fluids, if any) has been shed by the dagger at some point.

Possible Origins:  These blades are also commonly called Burglar's Daggers, but it remains unclear whether they were first created for a sneak-thief or an adventurer.  Both professions can certainly benefit from a light source that can't be seen by most other observers, whether it be wandering monsters or patrolling guards.  Their creation formula is fairly well known in the spellcasting community, and having one made on commission is almost as common as finding one in a treasure hoard or "inheriting" one from a former owner.

Complications:  These blades are coveted in both criminal and adventuring circles (which often overlap anyway) and may attract undesirable attention if your ownership of one becomes common knowledge.  Moreover, once the dagger has drawn even a drop of blood from a target, its light remains visible to that creature forever after.  Second-hand Delver's Daggers may have an inconveniently large pool of previous blood donors, especially since it's common for both adventuring parties and gangs of thieves to blood a dagger en masse so they can all operate under its light.

Design Commentary:  Almost prosaic as magic items go, but a useful tool and the potential limitations of "used" daggers that have been in circulation in an area for a long time can lead to some interesting wrinkles in a game.  Why does your seemingly-innocuous innkeeper see your dagger's light, anyway?  Was he cut by it in a bar fight long ago, or is he a retired thief who ran in a gang with a previous owner, or is the explanation something stranger?