This sword was forged in the ancient past at the request of a soldier who had to destroy an evil magician who had gained immortality.
The weapon to all appearences will appear to be a +5 sword until in battle when a qualified person swings the suddenly heavily unbalanced sword.
Plain looking dagger. However, when the dagger is seen in the light of an open flame Jamil’s hand print is on the hilt from where he gripped it in his death.
The local band of 'nasties' (goblins / orcs / whatever) lives in relative peace with the local population.
Along come the PCs and go through their usual heroic monster bashing routine, wiping out the nasties and pinching all their stuff, then continue on their way.
Problem is, they don't kill ALL he nasties. The survivors want revenge and, after spending a few months recovering, start to take it in their own inimitable style (which is not unlike that of the PCs come to think of it).
Next time the PCs are in the area they find themselves VERY unpopular with the townsfolk.