The story
Partial calque from Japanese 下(げ)駄(た)記(き)号(ごう) (geta kigō), alluding to the similarity between the shape of this symbol and that of a footprint from a geta shoe.
Etymology from Wiktionary, CC BY-SA 4.0.
geta mark
Today it means: The symbol 〓, used as a placeholder in electronic or printed text to indicate the presence of an ideographic character for which no glyph is available. Full definition →