This part was used in two sets, but it was printed:
Ah! Of course it was from Cars.
Also, if you click through to those sets’ inventories, you’ll see there’s another version with eyes printed. And then you’ll notice that there’s a brown version with Mater’s eyes printed…
93598 is the base number for the element, with the suffixes such as “pb01” reflecting the printed variants.
This is why Dan’s in MENSA and I’m not. I also tried to find the source of the piece and came up empty. The fact that BL lists zero sets for it doesn’t necessarily indicate that it never appeared in a set. One possibility – albeit unlikely – is that in the set it appeared it was incorrectly inventoried as a different but similar piece. I was able to quickly rule that one out. But another possibility was that it appeared in much older and/or rarer sets that nobody’s ever bothered to inventory for BrickLink, and for that I spent some time flipping through my Lego Collector’s Guide, and of course came up with nothing there either. So high five to Dan for good Lego detectiving.