1.
In a medium mixing bowl, combine the soy sauce, oil, Worcestershire sauce, brown sugar, garlic, chives and pepper. Reserve 1/4 cup of the mixture in a separate bowl and pour the rest into a large plastic resealable bag.
2.
Add steak to the bag, seal, and turn to coat. Refrigerate for 24 hours to marinate. Meanwhile, whisk the reserved marinade with the vinegar and keep in refrigerator for use later.
3.
Heat your gas or charcoal grill to high (Here's how to tell if it's high: Hold your hand about four inches above the cooking surface. After 2 to 3 seconds, the heat will force you to pull your hand away.)
4.
Oil the grill grate, using an oiled rag.
5.
Remove steak from marinade and place on the grill. Use these cooking times to cook your steak to medium: 2 to 3 minutes per side for a 1/2-inch thick steak, 4 to 6 minutes per side for a 1-inch thick steak, 6 to 9 minutes per side for a 1 1/2 to 2-inch thick steak.
6.
Take the steak off the grill and place in a shallow baking dish. Pour the marinade/vinegar mixture over the steaks, cover with foil, and let sit for 10 minutes. Serve.