Combine soy sauce, olive oil, lime juice, balsamic vinegar, Worcestershire sauce, garlic, brown sugar, black pepper, and red pepper flakes in a small bowl and whisk until the sugar is dissolved.

Place the skirt steak into a gallon-sized resealable bag and pour the marinade over it, squeezing out excess air before sealing.

Refrigerate the steak for 2 to 8 hours to allow the acids to tenderize the muscle fibers.

Remove the steak from the refrigerator 30 minutes prior to cooking to allow it to temper.

Preheat a heavy cast-iron skillet or outdoor grill to high heat until lightly smoking.

Remove the steak from the marinade and pat the surface thoroughly dry with paper towels to facilitate the Maillard reaction.

Sear the steak for 3 to 4 minutes per side, aiming for a deep charred crust and an internal temperature of 130-135 degrees Fahrenheit for medium-rare.

Transfer the steak to a resting board and tent loosely with foil for 10 minutes to allow juices to redistribute.

Identify the direction of the grain and slice the steak thinly against the grain at a 45-degree bias for maximum tenderness.