Habitual quotation marks are apparently not just for casual conversation, but there are also plenty of "written" "examples" of this humorous hand gesture.
Over at Jottings and Such, the blog of author Julie Stiegemeyer, you will find this post on The "Blog" of "Unnecessary" Quotation Marks.
Those of you with young children might know of Julie's board book series, Things I [See/Hear/Do] in Church. Check out all of CPH.org's offerings by putting "stiegemeyer" in the search box, and choosing "books" in the dropdown menu.
She also has writings for a more general children's audience. My favorite is Gobble, Gobble, CRASH.