The anarchists who apparently vandalized several cars and buildings in North Philadelphia on May Day aren't alone in their beliefs: Authorities have documented anti-gentrification vandalism, especially on the West Coast, for some time.

Tensions over gentrification have risen since the influx of tech companies and the resulting cost-of-living increases in places like San Francisco and Seattle, spurring regular protests — sometimes involving vandalism.

The magazine Mask, rounding up a list of incidents in the Bay Area, catalogued the vandalism of a bus carrying Google employees in 2013 — activists protesting gentrification smashed a back window during a protest. Mask describes itself as a voice for "antagonist youth."

The Department of Homeland Security released a 2013 memo outlining three arsons in Vancouver, British Columbia; Seattle; and Grand Rapids, Mich. — all at new development sites. Later, anonymous posters on anarchist websites claimed responsibility, and decried rent hikes and gentrification. All three fires were preceded by "a number of low-level criminal actions," including smashed windows and anti-gentrification graffiti, the department wrote.

Philadelphia police said Tuesday it was unclear whether the incident in North Philadelphia was connected to May Day. May 1 is traditionally a rallying day for anticapitalist and anarchist groups, dating to the 19th century and commemorating the Haymarket riot of 1886. That day in Chicago, someone lobbed a bomb at police during a rally for an eight-hour workday, and gunfire broke out. Several police officers and civilians were killed and dozens were wounded. The eight labor activists convicted of conspiracy in the aftermath — four of whom were executed — were pardoned seven years later by Illinois Gov. John Peter Altgeld, who wrote that there was no evidence they had been involved in the bombing.

In modern times, it's a day to express solidarity with the working class, and in Philadelphia, Monday's protests in Center City were peaceful and driven largely by mainstream groups — teachers' unions and immigrant rights groups.

"To lump [those arrested Monday night] in with people expressing constitutional rights would be premature and disrespectful of people who are legitimately trying to protest," said police spokesman Capt. Sekou Kinebrew. "People that did express themselves in a lawful manner -- that's as American as apple pie. What we saw last night was a crime. Multiple crimes."