This rune is a relic of the Legacy Chain. When an unsuspecting villain crosses one, it summons an Animated Stone, two or three Fire Imps, and a Phantasm (called "Champion of Light"), as are the three types of Legacy Chain troops. Defeating these summoned mobs won't net you any Infamy or Experience at all. The rune is also targetable and has the same Hit Points as a Minion of the same level. Apparently, if the rune is attacked and its life bar drops to 50% the pets are summoned and aggro on the attacker as well.
The Eihwaz Runes are found:
These strange runes glow ominously with unstable mystic energy.