Six skywriting planes were used in the anti-Trump stunt above the annual Rose Parade in Pasadena, CNN said.
Other messages hitting out at Trump, the frontrunner for the Republican nomination for the White House, included: “Anybody but Trump”, “Trump loves to hate”, and “Trump is delusional”.
It was not immediately clear who was behind the protest, images of which were posted on social media.
However, CBS News said an Alabama businessman, Stan Pate, was behind the airborne protest targeting.
A CBS reporter interviewed Pate on the air after the parade.
Pate did not immediately respond to a request for comment from Reuters.
But he told CBS News in the interview that he considered the billionaire candidate to be despicable, and that “this is just the start”.
Pate said he had paid for anti-Trump messages at the recent Cotton Bowl, Sugar Bowl and Orange Bowl college football games.
“Other candidates can’t get in the gutter with him,” Pate said. “I can and I will if that’s where he wants to continue to go.”
CBS reported that Pate, who like Trump is a real estate developer, has donated to Democratic and Republican candidates in the past.
In the current primary campaign leading up to the November 2016 presidential election, he has contributed to the campaign of Republican White House hopeful Marco Rubio.
Trump, whose controversial run for the White House has seen him call for a ban on Muslims entering the United States, did not make any immediate response.
The billionaire real-estate tycoon and reality TV star, who has said that Mexico is sending rapists and other criminals into the US, greeted the 2016 election year by proclaiming on Facebook: “2015 was a very special year, and I am grateful for your support!
“We are making history together! The silent majority is no longer silent.”
Security on the ground for the parade in Pasadena, north of Los Angeles, had been tight.
More than a  half million spectators thronged the 5-1/2-mile (9km) route of the 127th Tournament of Roses Parade, followed by the 102nd Rose Bowl college football game.
Spurred by last month’s deadly mass shooting in nearby San Bernardino, more than two dozen federal agencies joined forces with police for the largest security operation in the history of the Rose Parade and Rose Bowl.
Many of those in the crowd looked skyward as the aircraft left their short-lived statements against a deep blue backdrop.
The planes circled for almost an hour after the parade of flower-adorned floats and marching bands finished.