In a small bowl, combine the salt, garlic powder, onion powder, oregano, paprika, pepper, thyme, and cayenne. Mix well.
Preheat the grill to high. Scrub the grill rack with a grill brush. Use grilling tongs to dip a wad of paper towels in some vegetable oil and use the oil-dipped paper towels to wipe down the grill rack.
Pat the swordfish steaks dry with clean paper towels. Brush the fish with the olive oil and sprinkle the blackening rub evenly on all sides of the fish, pressing it into the fish.
Grill the swordfish for 2 minutes, then flip the fish and cook for another 2 minutes. Flip the fish once more, turning them 90 degrees or a quarter of a turn, so that the grill grates are perpendicular to the first set of grill marks. Grill for another 2 minutes, then flip once more, again rotating the fish so that you get cross-hatched grill marks. Grill for another 2 minutes, or until the swordfish steaks are just barely cooked through. To test press with your finger; the fish should flake into large chunks.
Let sit for a few minutes before serving. Serve hot or warm with lemon wedges and salsa, if desired. You can also serve the swordfish sliced.
Notes
Trim away most of the bloodline, the dark red section of the swordfish before cooking. It has a stronger flavor than the rest of the fish. You should do this before cooking if possible, or remove it or avoid it once cooked.
Avoid fish with a brown bloodline; it should be a fairly intense red.
Make sure your grill grates are clean and oiled and the grill is very hot before putting the fish on.
Depending on the thickness of your swordfish, you may want to flip it one, two, or even three times. Thicker swordfish (over an inch thick) can be flipped up to three times, allowing you to get those nice cross-hatch marks without overcooking the interior. If your fish is thinner, you may only want to flip it one or two times to prevent the fish from drying out as the outside takes on a nice browned color.
The internal temperature for medium grilled swordfish is about 130 to 135 degrees, for medium-well look for an internal temp 135 to 140 degrees, and if you prefer your fish cooked to well-done, cook it to 145 degrees. If you are cooking your fish to well-done, remove it from the grill the moment it hits that 145 internal temperature, or it will dry out.