The police in HBO's Watchmen wear masks and there's a very good reason why they need to. Executive produced and written by Damon Lindelof, Watchmen is an ambitious continuation of the classic graphic novel by Alan Moore and Dave Gibbons (but not the 2009 film by Zack Snyder). Lindelof's series is a self-described "remix" that furthers the complex political themes of Watchmen but changes the setting to present-day Tulsa, Oklahoma - a place where both the police and their enemies conceal their identities with masks.
In the world of HBO's Watchmen, Tulsa continues to reel from the aftermath of a real-life event: the Tulsa massacre of 1921 where white residents attacked the African American businesses and people in the prosperous Greenville district, which at the time was known as the "Black Wall Street". Nearly a century later - and 30 years after Adrian Veidt aka Ozymandias used a giant squid monster to attack New York City, which averted World War III - Robert Redford is now President of the United States and he instituted legislation (known as "Redfordations") which are reparations for victims of racial injustice in American history - including the Tulsa massacre. However, Tulsa is still a hotbed of violence thanks to the Seventh Kavalry, a white supremacist cult modeling themselves after Rorschach.
The Tulsa Police Department now wear masks to protect their identities from terrorist organizations, including the Seventh Kavalry. In a violent incident called (somewhat ironically) the White Night three years prior, members of the Seventh Kavalry attacked the police in their own homes; most were killed but many cops who survived quit the Force. However, the police who remained rallied under Chief Judd Crawford (Don Johnson). They instituted strict new rules to protect themselves and their families, including a policy to hide their identity by always wearing masks in public. While most police still wear traditional costumes with added yellow masks, others have adopted more colorful identities, such as Detective Angela Abar (Regina King), who took on the codename Sister Night; other masked Tulsa cops include Looking Glass (Tim Blake Nelson) and Red Scare (Andrew Howard).
Tulsa's masked police became legal thanks to another act of Redford, the Defense of Police Act (DoPA), which allows police to hide their faces behind masks because they were being targeted by terrorist organizations. DoPA protects the police who were victims of the White Night and every other officer who could be victimized in the future. However, while the masks protect the police's identities and provide an intimidating aura, some of their other regulations are very restrictive.
The Tulsa Police use stun batons and other non-lethal weapons; however, their use of guns is strictly regulated and the cops have to request authorization to use firearms, which can only happen if a police officer's life is in imminent danger. In Watchmen's pilot, Chief Crawford authorized Article 4 in response to a Cavalry member murdering a police officer; the cop in charge of "buzzing out" the guns, Panda, argued against the emergency 24-hour authorization of firearms until the assembled police officers agreed that their lives are under "direct and immediate threat". Incredibly, the Tulsa P.D.'s raid on the cattle ranch where Seventh Kavalry were hiding out included the use of an Owlship, the signature vehicle of the second Nite-Owl!
In terms of Watchmen's history, Tulsa's masked police harken back to the original Nite-Owl, Hollis Mason, who was a New York City police officer and he adopted his costumed identity after he was inspired by the appearance of Hooded Justice. There's even a copy of Mason's autobiography Under The Hood on Crawford's desk. Further, Zack Snyder's Watchmen movie made a change from the graphic novel: Hollis (Stephen McHattie) told his protege Dan Dreiberg (Patrick Wilson) that the Minutemen were originally former cops who donned masks to fight back. It's easy to draw the through-line from Nite-Owl to Sister Night and her compatriots in HBO's Watchmen.
Watchmen airs Sundays @ 9pm on HBO.