The bright red bricks painted onto the two guardhouses flanking City Hall are supposed to encourage optimism and liberalism, according to the Public Art Fund, which sponsored the art installation by Richard Woods. But City Councilmember Tony Avella, a mayoral candidate, objected to the whimsical interpretation, saying that the installation, called “wall and door and roof,” trivializes security. “Everyone who sees this monstrosity agrees it is absolutely ridiculous and an insult to the police officers who man this post,” Avella wrote in a press release last week. The notable exception, which Avella pointed out, is Mayor Michael Bloomberg, who called the painted bricks “cute.” Another exception was a police officer posted near one of the booths on a recent afternoon. When asked if the cartoonish bricks offended his sensibilities, the officer shrugged and laughed. “I’m fine with it,” he said. The brick-painted facades will be in place through September.