Une discussion sur la liste typo a utilisé ponctuation dans la marge, ponctuation pendante et même « hanging punctuation ». J’ai donc l’impression qu’il n’y a pas (au moins qu’il n’y avait pas à l’époque) de traduction consacrée. La « justification optique » aussi présente dans cette discussion est plus large, la ponctuation pendante est un moyen d’y arriver.

Try Linguee when you want to translate technical phrases. It’s a database of bilingual texts in various language pairs, including French and English.

There is one hit for hanging punctuation: “ponctuation hors justification”, found in a Quark, Inc. brochure. I don’t have an official reference to offer, but several manufacturers of typographical software (Quark, Adobe) have used the term, as have books about CSS, so I would guess that it is indeed the standard translation.

The phrase “ponctuation hors justification” gets a decent number of hits on Google, unlike “ponctuation dans la marge” (which has a single relevant hit), “ponctuation pendante” (which isn’t much better, in spite of its obviousness as a literal translation), or “ponctuation suspendue” (most of the hits are unrelated).

The question was asked in passing on the typographie mailing list, with no conclusive answer.