BOSTON, Massachusetts (CNN) -- Electronic light boards featuring an adult-cartoon character triggered bomb scares around Boston on Wednesday, spurring authorities to close two bridges and a stretch of the Charles River before determining the devices were harmless.

Turner Broadcasting Co., the parent company of CNN, said the battery-operated light boards were aimed at promoting the late-night Adult Swim cartoon "Aqua Teen Hunger Force." The devices had been placed around Boston and nine other cities as part of an "outdoor marketing campaign," a company statement said.