PARIS — No one seems to know just what is meant by the “quenelle,” the vaguely menacing hand gesture invented and popularized by a French comedian widely criticized as anti-Semitic, but it is clearly nothing very nice, and it appears to be spreading.

Fans of the performer, Dieudonné M’Bala M’Bala, send him photos of themselves performing the gesture in front of historic monuments, next to unwitting public officials, at weddings, under water and in high school class photographs, but also, increasingly, beside synagogues, Holocaust memorials and street signs displaying the word “Jew.” At least one young man appears to have posed for a quenelle outside the grade school in Toulouse where, in 2012, four Jews were killed by a self-proclaimed operative of Al Qaeda.

Jewish leaders, antiracism groups and public officials have pointed out that the quenelle, which is also the name of a fish dumpling that is a regional French delicacy, strongly resembles a downward-facing Nazi salute. Mr. M’Bala M’Bala, who goes by Dieudonné, insists it is nothing more than an “antisystem” joke for his initiates, most of them young men, some from the disaffected immigrant suburbs, some from the xenophobic far right.

Still, when he seethes against “the system” on stage or in his popular Internet videos, Mr. M’Bala M’Bala generally points to a supposed cabal of Jewish “slave drivers,” secret rulers who cloak themselves in the memory of the Holocaust. The performer, the son of a black Cameroonian and a white Frenchwoman, often argues that Jews have unfairly claimed a monopoly on the status of “victim.”