I don’t think there is. The transgender flag is for anyone that is trans. There are transfemme and transmasc specific flags (though they aren’t in Unicode so they can’t be used like I do the trans flag). Do note that transfemme / -masc does not mean transgender woman and man, they describe how one would like to present and/or express themselves.
That would be counted as “non-voting” (see Ukr, Afg, Ven). Abstain means the rep was there and voted “abstain”