I noticed a number of other head stickers today but only took a picture of this one. I'm not sure if they're numbered prints, or what "138" indicates about this particular sticker. I'll try to look more closely at another one and see if the same number is on it, or another.
The more I look at this sticker the more unsettled I feel about what I think is the drawing of a head and face. Is his mouth open or closed? There are no teeth, but that would be one big lip if it's a closed mouth. Is that a moustache on the upper lip? Most unsettling of all is the nose. There's one line too many - it looks like the artist drew two noses on accident. Or is it on purpose? I'm guessing the face is wearing spectacles, hence the undefined eyes and the frame crossing the bridge of the nose. That guy has some big earlobes. And why is he smiling like that? What's to be happy about? Happy that he's #138 I guess.