I thought this face was just an Obunai thing, but then I saw it in Chouriki Robo Galatt episode 1 as well. Serendipity finally led me to its origin - it's typographic symbol BA-90. Some kind of old meme I guess. The Unicode equivalent is U+1F31D Full Moon With Face. It was used in computer game magazine LOGiN (under the name pogemuta mark) and in anime magazine Gekkan OUT. As well as a lot of manga.
Edit: just saw it in the new Mahoujin Guruguru too