I do believe that it stands for European Sport Sedan. I may be wrong. I have been before.
You sir, are correct. It was a model offered in 79 & 80 only. It came with the black accents around the side windows, blacked out grill & headlight buckets, windshield trim, black stickers on the all glass back hinges, and I think a few other things. It also had round gauges in it, rather then the square gauges like regular pintos, and I think it also came with the 3 gauges in the dash above the radio.
It was made to look similar to the European cars at the time, and try to steal a little bit of sales from them.
Not sure how many were made, can't find any numbers on them. I do know they aren't too common though. Not only were sales lowest in 79 & 80 for the pinto, but being that it was a "special" model only adds to the rarity of the car.
Me personally, it is important to me, not cause its rare or cause Pintos are a "fad" right now, it's because of the fact that it has been in my family since late 1980, and the fact that it was a summer father-son project. I learned to drive stick on the car as well. Had to learn in 2 weeks so that I could drive it to New York for a car show (roughly a 3 1/2 hour ride, one way). I love the car more than anything else, and I will have the car as long as I am alive.