Tried a Cooks Illustrated recipe today.  The skirt steak is smeared with a paste made from 1 Tblspn oil, 2 tsp minced chipotle pepper, 1 tsp of the chipotle adobo, 3/4 tsp cumin, and 1 1/2 tsp salt (I left out the salt as I'd salted the skirt steak the night before and wrapped it tight in saran wrap).  Grilled over a very hot fire along with a large tomato and two jalapeños, mesquite smoke.  
 

 
The recipe suggested flipping the steak every two minutes, to keep one side from shrinking more than the other and cupping the steak; I had no issue with that.  
 
I chopped the grilled tomatoes, and minced the jalapenos, added a crushed garlic clove, and a bit of salt, mixed it up in a bowl while the steak rested.  Also prepped Tillamook 4-cheese mexican grated, chopped some fresh cilantro, chopped a fresh plum tomato, lime wedges, and had some guac on hand.   (Slightly over-) toasted some flour tortillas.  
 

 
Steak was cooked perfectly, red but warm in the center and a very good crust.  The tacos were delicious, but there was no heat whatsoever.  I'm thinking the blackened crust the meat had, was just burnt chipotle/cumin mixture.  Next time I'll either add the paste the night before, or spread it on at the end of cooking.  Tasty, nonetheless.