“The first two appear to be standard sign language,” Rabbi Margolin said of the signs in the letter to the rector, Rik Van de Walle. “If the aim of this project was to embellish or add to the standard definition, it has certainly managed to so, in the most stereotypical and racist way imaginable, by focusing on side-locks and, worse still, gesticulating a hooked nose to describe a Jew.”

But the university, which has about 44,000 students and is publicly funded by the Flemish government, has declined to take any action. It said that it had discussed the complaints with the researchers who created the dictionary. But in a statement on Friday that was approved by Mr. Van de Walle, the university described the controversy as a purely “scientific issue.”

It said that in creating the dictionary, researchers merely “register and describe the signs that are used in the Flemish sign language.” It added: “They don’t take position on these signs, and don’t cast a value judgment on them. This is what lexicographers do.”

The controversy comes amid a wider rise in anti-Semitism across Europe. And Belgium has been criticized for the persistence of blackface imagery as cultural themes and for other tactics seen as punishing religious minorities.

One of the most popular festivals for Belgian children is St. Nicholas Day, on Dec. 6, when the saint brings presents for all the good children and the bad ones are punished by his helper, a character called “Black Pete,” who wears blackface makeup.