The skies above the Hiroshima Peace Memorial were perfectly clear last Tuesday morning — until a small plane appeared and started writing in smoke a Japanese word that could be translated as “Bang!”

In an article the next day, the local Chugoku Shimbun reported it was flooded with phone calls from citizens who had seen the skywriting, which was obviously designed to remind them of the atomic bombing of the city 63 years ago. Most callers, the newspaper reported, expressed “displeasure.”

It turns out that the stunt was the latest project by artist group Chim ↑ Pom, whose shock tactics The Japan Times covered this summer. They were filming the word as it floated in the sky above the memorial that they planned to submit for a solo show at Hiroshima City Museum of Contemporary Art next month.

But not any more. The stunt was denounced by Sunao Tsuboi, head of an association of atomic-bomb victims’ groups in Hiroshima, and attracted vitriolic criticism on the infamous 2Channel Web site, resulting in Ryuta Ushiro, the normally footloose leader of Chim ↑ Pom, offering a public apology. The exhibition was also canceled.

The Japanese word the artists wrote in the sky was “pika” — the kind of term used in manga to describe bright flashes of light. It is also used in popular literature to describe the blinding flash of an atomic-bomb explosion. Ushiro said he had hoped the work would draw attention to perceived ignorance among younger generations about the atomic bombing.

But that wasn’t enough to placate the detractors. Tsuboi commented wryly that the artists were entertaining themselves at the expense of others and that they should think more seriously about the issues involved. 2 Channel was awash with complaints, from resentment that Tokyo-artists were exploiting Hiroshima to simple statements of hatred.

With that abuse, the public apology and, above all, the canceled exhibition, Chim ↑ Pom, who had enjoyed a meteoric rise of late, have suffered a big setback. And it has been at the hands of one of this country’s long-standing, unique and formidable artistic taboos: facetiousness with respect to the atomic bombings.

Journalist Makoto Murata, who has been observing the Japanese art world for 30 years, says “the atomic bombings have always been a sensitive issue,” noting that 10 years ago the Chinese artist Cai Guoqiang ran into similar difficulties when he tried to hold one of his famous explosion works in Hiroshima. (His international reputation has now made such projects possible.)

There are other artistic taboos in Japan that outsiders might find puzzling. The Emperor is accorded such protection that he is no doubt the envy of royal families the world over. In 1986, Nobuyuki Oura’s “Holding Perspective,” a collage series depicting him alongside, for example, tattooed buttocks, caused a stir when it was purchased by the Museum of Modern Art, Toyama. Over 300 rightwingers turned up at the prefectural assembly demanding the works be sold, and they ended up getting their way.

Murata remembered that in the mid 1990s, too, another argument flared when a similarly “disrespectful” painting by Kikuji Yamashita was being considered for a major retrospective of the artist. The show ended up going on without it.

Japan’s museums have always been averse to sexually explicit art, too, says Murata. “Museums just wouldn’t show such work, exercising jishu kisei — or self-regulation or restraint.”

Four years ago, the Yokohama Museum of Art was forced to pull a sexually confrontational exhibit from its walls. The video work, by Tadasu Takamine, showed a disabled person being assisted in masturbation.

Still, Murata says the Takamine case demonstrates that over the last few years Japan’s museums have become more willing to confront their nation’s taboos.

“In the past, museums just wouldn’t have shown such work,” he says. These days they might show it, but try to circumvent problems by issuing warnings to visitors about the content.

The Mori Art Museum adopted that approach with shunga — pornographic ukiyo-e (genre painting) woodblock prints — in 2003. The Yokohama Triennale has done the same this year.

While purists might fret that such warnings undermine the very shock that such art is likely trying to harness, it seems there is currently no other option.

There are indications that advance notice might have saved Chim ↑ Pom, too. Among the shouted abuse online were comments asking why the artists and the museum hadn’t informed the victims’ groups in advance. The suggestion is that with fair warning, even their understandably delicate sensibilities might have been able to cope with the affront.