Po said the MPD was studying security-camera footage to identify those responsible. "Those identified will be charged with malicious mischief. Even their leaders, who are identified, will be included in the criminal charge," he told the Inquirer.
Security was beefed up at the US Embassy to prevent the recurrence of the protest.
In Floridablanca town, Bayan leaders said there were some 400 protesters but the local police placed the number at less than 200.
About 50 PAF personnel blocked the base's main gate when the activists arrived at 11:20 a.m. A fire truck was seen near the gate.
The protesters painted anti-Balikatan slogans, such as "US troops out now," "No to Balikatan," and "Junk VFA (Visiting Forces Agreement)," on the concrete fence of the base in San Jose village.
The PAF did not disperse the protesters who held a brief program condemning the military exercises.
"The Balikatan is but part of a bigger design to make US troops permanent fixtures in the Philippines, even without any formal basing treaty," Bayan secretary general Renato Reyes Jr. said in a statement.
"We duly respect their freedom of expression and we congratulate them for the peaceful rallies," said Lieutenant General Anthony Alcantara, Norther Luzon Command chief.
On Sunday, the eve of the anti-Balikatan protests, police in Angeles City released five Anakbayan members after filing a complaint for mischief against them. The Anakbayan members were arrested on Saturday night after they were caught posting anti-Balikatan posters in the city.