you need a low flame for marks.
You need the seasoning to make a crust.
That is BLACKENING at it's finest. Burnt meat makes a crust. I only use S&P and not like a blackening amount.
Like THp says, heat makes a sear (crust).
But now I am drunk and probably sounding argumentative so I'll shall stfu!
I use cast iron grates and charcoal, and oil.
Then coat the steaks with oil (I use extra virgin olive oil or canola oil. Depends on my mood)
That is BLACKENING at it's finest.
Yuppers!