The inscription on this painting, which today is held by the Wien Museum (Inv. No. 158.809), was first published in 1995 by my friend, the late Irving Godt as follows:
This flawed transcription ("METASTASIO", "VINDIBO") was then also mistranslated by Godt: "Marianna Martines, Pupil of P. Metastasio; born in Vienna, 4th day of May 1744, Member Academia Filarmonica."
When Melanie Unseld was working on her book Mozarts Frauen. Begegnungen in Musik und Liebe and spent time in Vienna "to make original sources the basis of her book" (as she proudly claimed in a press interview), she visited the Wien Museum's deposit to take a look at the Martines portrait. Her "on-site inspection in Vienna" (as she described this excursion) yielded meager results: although her book contains a nice color picture of Maron's painting on which the Latin inscription is perfectly legible, Unseld simply copied Godt's flawed transcription from the 1995 Journal of Musicology. In the review I wrote of Unseld's book in 2007 for the Mozart-Jahrbuch 2007/2008 (which was not published until November 2011[!]) I pointed out this mistake and noted that Unseld should have copied the inscription from the painting proper instead of using Irving Godt's old transcription. It turned out that Unseld was able to even go one better. In the February 2011 issue of the Schweizer Musikzeitung she published a short article on Martines in which she not only repeated Godt's mistakes, but also presented a curious new translation, turning the poet Pietro Metastasio into a "Padre Metastasio":
When in February 2012 Sony Music published the CD Marianna Martines: Il Primo Amore with cantatas and concertos by Martines, Unseld not surprisingly repeated her "Padre Metastasio" gem in the booklet (and note that Maron's portrait all of a sudden has been redated to 1780):
We can safely presume that neither Irving Godt nor Melanie Unseld ever studied Latin. Otherwise they would have realized that the first transcription and its translation were flawed already. The missing genitive in "Metastasio alumna" is the kind of Dog Latin that should be unworthy of any musicologist. Likewise, the translation of the date with "4th day of May" reveals a certain unfamiliarity with the Roman calendar. Maron's Latin inscription on the Martines portrait reads as follows:
MARIA ANNA. MARTINES. P[ETRI]. METASTASII. ALUMNA
NAT[A]. VINDOBO[NÆ].[ANTE DIEM] IV. NON[AS]. MAI[AS]. MDIIXLIV. ACAD[EMIÆ]. PHIL[HARMONICÆ]. SOC[IETATIS].
Maria Anna Martines. Pupil of Pietro Metastasio
Born in Vienna, on the fourth day before the Nones of May 1744, [member] of the Academic Philharmonic Society.
Together with her four brothers Marianna Martines was ennobled by Maria Theresia on 23 January 1774. Here is the coat of arms of the Martines family:
And since he somehow caused the whole confusion, Anton von Maron gets the final word with his signature and seal from 1764 (A-Wsa, AZJ 210/9).