In Tolkien's works are notorious elvish blades like Sting that glow when there are orcs or goblins nearby. Although Tolkien's work is profoundly original as a whole, the author himself always attempted to integrate ancient elements of European legends and folklore, especially from the northern peoples.
Can you let me know if in those legends and myths there is some weapon with a sharp edge (a sword, a dagger, an arrow) able to shine for warning its owner of the proximity of enemies? If not in those legends, are there any other legendary weapons in other cultures that can warn to their masters?