According to a story in the Guardian, "[r]esidents of Liverpool - the city that bred her late husband, John Lennon - lodged complaints about her photograph of a naked woman hanging from a war memorial." The picture, which has been taken down, was a large banner across the St. Luke's church. People were upset because "Ono's image, entitled My Mummy Was Beautiful, stood over the steps of the church which was left as a shell after it was hit by Nazi incendiary bombs." She said that the image was a tribute to John Lennon's mother, Julia. Ono is also responsible for "[p]ictures of shaved pubic hair and nipples also appear on billboards on Church Street, in the heart of the city's shopping district."
I can think of no better tribute to someone's mother than a picture of a naked breast draped over a bombed out church/war memorial, though the billboards featuring shaved pubic hair and nipples might be just a tad much.