Here are two versions. I had a vegan friend over and made the one that called for seaweed since it has an oceaney (made up word) flavor. I used kombu since I always have it on hand.
Thanks, Susan W!
worcestershire sauce has similar taste profile. here's one commercial and one home made version
And/or if can't find vegan worcestershire in store nor want to make it, good tamari or soy, for similar not-identical umami flavor hit.
ps. sorry forgot to mention both edward & sons, and Martha Stewart versions are vegan.
Thin soy sauce is a pretty perfect substitution. I use Dragonfly brand: http://www.templeofthai.com/food/sauces/thinsoy-5133231037.php