.notdef is a glyph shown when an application cannot find any glyphs corresponding to a Unicode codepoint. This is usually a narrow box (nicknamed tofu), sometimes crossed out or containing a question mark.
Many Toki Pona fonts have unusual
.notdef glyphs. This has been done both for practical purposes and for fun. For example, in sitelen pona, the typical
.notdef glyphs could be mistaken for lipu, lipu ala, and lipu seme (lipulipu-alalipu-seme). An alternative used in multiple fonts is a square ijo ni li seme? (ijo-ni-li-seme), interpreted as the font or application asking the user "What is this thing?" about the unsupported glyph.