2 teaspoons cumin seeds
3 garlic cloves, peeled and sliced
1 teaspoon kosher salt
1 teaspoon crushed red pepper flakes
While the steak is cooling, toast the cumin seeds in a small skillet over medium-low heat, shaking the constantly so they don't burn or stick, just until they are fragrant, about 3 minutes. Let them cool.
Squeeze the juice from the limes into 1-gallon heavy plastic resealable bag. Add the cumin seeds, garlic, 1 teaspoon salt, and the pepper flakes and swish the marinade around to dissolve the salt.
Slip the cooled steaks into the marinade, press out most of the air from the bag, and seal the bag very tightly.
Refrigerate the beef for at least 4 hours or up to 1 day, turning the bag several times.