Combine the vinegar, soy sauce, Worcestershire sauce, and mustard seeds in a large resealable plastic bag. Add the steaks and seal the bag. Refrigerate at least 30 minutes and up to 2 hours, turning the steaks occasionally.
Prepare the barbecue for medium-high heat or preheat a grill pan over medium-high heat. Drain the marinade from the steaks. Grill the steaks to desired doneness, about 6 minutes per side for medium-rare. Let the steaks rest for 10 minutes. Cut the steaks crosswise into thin slices.
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