About 70 student activists took police and embassy guards by surprise early Monday when they threw blue-and-red paint at the seaside mission's main gate and scrawled "U.S. troops out now." They also chipped away letters from the bronze signage and burned a mock American flag.
No arrests were made as protesters outnumbered police and later walked away.
Thousands of U.S. and Filipino troops are taking part in 12-day combat and disaster drills. This year they are taking place in the western Philippines, where tensions with China have been rising over disputed territory in the South China Sea.