62Bricks

I don't find any evidence that it was ever officially used in a set or idea book for SNOT, Fugazi. There were a few versions. I think the earliest version was the one that had a pointier, longer sloped sill on the front. Other variants had the sloped sill "chopped" off to give it a blunt face. There were variants to the back, as well. One version had an open slot on the back with smooth inside walls that were 1 stud apart. These would grip a stud. Another variant had thinner walls on the back that were thicker at the bottom. The opening on the back of these was just a little larger than a stud, I think, but it's starting to look more like the modern headlight brick. Here's a picture of the backs from LDraw: Seem to be having trouble linking the image...

The 1x4x2 fence piece has been around since the late 60s, and was certainly designed to be used as a SNOT piece. The earliest official application of it in that way that I find is the 1974 Tractor with Trailer. It was used in the gear accessory set from the same year, also as a SNOT piece SNOT techniques were in evidence in the earliest idea books produced by LEGO in the 1960s. I would agree with Peewit's suggestion that perhaps the earliest explicit SNOT elements were the studded wheels, which provided a plane of studs 90 degrees from the orientation of the axle-holder brick. There is also the precursor to the 4070 headlight brick, which was the old 1x1 window brick. There's an early documented use of the classic plate-wedge in the clock on the train station in this 1966 idea book. From the earliest sets and idea books, LEGO has encouraged building in different planes. Look at the airplane models from this 1964 idea book: And look at the buoys on this page from the same book. They're completely upside-down.