Capt. Chris Fowler, who's in charge of the department's response to the demonstrations, said that if people have a message to get out, they should get it out safely and peacefully. Police will escort a permitted march for immigrant and worker rights Thursday afternoon, as well as a later unpermitted march by anti-capitalist protesters.
"Welcome to May Day," Fowler told reporters. "Come downtown, enjoy the atmosphere, enjoy the day."
The department's blog said vandals spray-painted a few businesses early Thursday in the Capitol Hill neighborhood - a car dealership, bank, restaurant and "the neighborhood headquarters of the oppressive regime at the United States Postal Service."
Officers also found "Kill SPD" painted on the bank, and a flier was circulated calling for killing officers.
"There are issues with our police department. But when people say we ought to kill police, that's unacceptable," Mayor Ed Murray said.
Violence has plagued May Day in Seattle over the past two years, with protesters and police officers squaring off in the streets. Last year, police used flash bangs and pepper spray and arrested 18 people from a crowd that pelted them with rocks and bottles. Eight officers were injured. On May Day 2012, masked marchers dressed in black broke windows and doors on downtown banks and stores and tried to set a fire at a federal building.
Thousands are expected to attend the 14th annual march by immigrants, who will be joined by groups calling for a $15 an hour minimum wage in the city. The march begins at 3 p.m. at St. Mary's Church and ends with a rally at the downtown Westlake Park.