The sign for "big" and then the sign for "foot". At least that's the way I learned it in my college ASL (weird that it came up, but it did, because for our finals, we had to sign a song and a commercial. One guy did the Jack's Links commercial "Messing with Sasquatch". Heck of a coincidence, lol. I just googled it, too, and didn't find anything more recent.