Right now, there are many police cruisers, both marked and unmarked, parked on Avenue Louis Pasteur. A large number are parked illegally, either in no-parking zones, bus stops, and even blocking crosswalks (in front of Boston Latin, a school zone.) This is an area where both the MBTA and MASCO run a large number of shuttles and need all the room they can get just make the turns. The State Police, Northborough, Danvers, and Boston were among the 'representatives' who showed up with marked cruisers. The unmarked cruisers and personal vehicles had various "I'm a cop" signs- raid jackets in windows, ticket books on dashboards, radios left in plain sight, or emergency lights.
They are attending a conference in Harvard Med's New Research Building, held by IACP, regarding Project Safe Neighborhoods. IACP is a police chief association, so there are probably a bunch of chiefs amongst these lawbreakers. Of note- there are multiple pay lots within 1-2 blocks, and public street parking within a few blocks.
Update: photos from twheaton. More welcome, especially showing plates and the signage showing they're illegally parked.