NEW YORK — Santa Claus, giant cartoon balloons and whimsical floats were protected by sand-filled dump trucks and bomb-sniffing dogs as the Macy's Thanksgiving Day Parade wound its way through the streets of Manhattan under heavy security.The annual spectacle went off without a hitch Thursday, with thousands of spectators and more than 3,000 police officers lining the streets amid an air of uncertainty about the possibility of an extremist attack."There are so many police officers out here you can't help but feel safe," said Sarah Bender, who brought her two young sons to watch the parade. "It's a day to have fun, watch the balloons and celebrate with your family. You can't spend your life worrying about what could happen."While authorities had said there was no confirmation of any credible threat, they stepped up safety measures in the wake of the July cargo truck attack on a holiday crowd in Nice, France, and a recent posting in an English-language Islamic State group magazine that called the Thanksgiving parade "an excellent target."Revelers cheered and yelled, "Thank you!" to officers along the route Thursday, giving special attention to the New York Police Department marching band.Spectators sometimes stood 10 deep to see the parade and its signature giant balloons, including Ronald McDonald, SpongeBob SquarePants, Charlie Brown and other characters.