As police investigate people still enjoy a Grant Park art installation that was vandalized with graffiti. (Nuccio DiNuzzo/Chicago Tribune)

An art installation of 26 life-size human sculptures at Grant Park was vandalized overnight when graffiti taggers left their signatures on 18 of the statues.

The public art exhibition titled "Borders" are on loan from Icelandic artist Steinunn Thórarinsdóttir and were installed in August in a garden named after Sir George Solti at East Jackson Drive and South Michigan Avenue.

Bob O'Neill, president of the Grant Park Conservancy, said he saw the statues with the graffiti this morning and said the taggers used two different signatures, leading him to believe there may be several people at work.

O'Neill believes that the statues were hit either late Friday night or in the wee hours of Saturday. O'Neill reached out to the Central District Chicago Police commander to alert him of the vandalism.

He said he is in the process of filing a police report. He said the statues were to have been returned to the artist but the artist allowed the statues to extend their run until October after being told of the installations' popularity.

He said people, especially children, like to go up to the statues and pose with them for pictures and touch them. He said this is the first time they have been vandalized here.

This morning O'Neill overheard a young boy going up to his mother and telling her that there was graffiti on a statue and watched as the mother took a picture of her son next to a statue bearing the tag.

"It's a bad image of Chicago and for artwork," said O'Neill. "We all worked really hard to put them here. It's upsetting when so many of them are tagged with grafitti."

He said he reached out to the park district to try and get them to clean the markings but he said he hopes that cleaning the statues does not further damage the artwork.

The statues are expressionless, in either silvery, gleaming aluminum or rust-stained iron. Each aluminum piece weighs 180 pounds and each iron piece weighs 440 pounds.

The artwork, which took two years to complete, was first installed in 2011 at Dag Hammarskjold Plaza near the United Nations Headquarters in New York. Thórarinsdóttir said last year that she consciously placed her figures in that socially and politically charged environment, and her choice to install them in Chicago's Solti Garden was just as careful and deliberate.

Days before "Borders" was installed, she sat on one of the garden's benches for hours considering how her sculptures would fit into her surroundings. She recalled listening to the languages spoken by people of all sizes and colors, and she knew she had found her gallery space.

"I wanted the installation to relate to people that wherever we come from, whatever our life experiences, we're all connected in shape and spirit," she said last year. "This garden was my first choice, a natural choice."

The park, situated just south of the Art Institute of Chicago, provides the intimacy of an enclosed room in an area heavy with foot traffic. The lattice of tree trunks forms the walls, branches rising up into a leafy canopy.

O'Neill said he wants attention to this vandalism especially since it happened on Michigan Avenue.

"No one should feel that comfortable, coming right on Michigan Avenue and spending that much time to tag 18 sculptures," O'Neill said.

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