"Clocked you going over 90 in a 65. I have a six-minute video of you driving like an [expletive], and pulled up next to you and took your picture.
"Try fighting this … I dare you! What happens when you try and run an officer's truck off the road … Hope it was worth it. See you in court," the threatening missive concluded.
The driver ignored the note and appealed the citation, according to prosecutors.
Growing suspicious, an investigation was launched after authorities couldn't determine who wrote the ticket, which had an illegible signature.
The officer identification number on the ticket didn't match with any working officers.
Eventually, State Police discovered that the ticket book came from the Boston Police Department and had been signed out to Curtis, records show.
After he was confronted by investigators, he admitted to writing down the driver's licence plate before mailing him a ticket "as sort of a warning".
Curtis, who joined the department on September 11, 2017, has been placed on administrative leave without pay following his arraignment, Boston Police Sergeant Detective John Doyle told The Post.
He pleaded not guilty on Tuesday during his arraignment in Suffolk Superior Court to charges of forgery, witness intimidation and misleading an investigation and was released on his own recognisance.
"These allegations outline an abuse of power by an individual responsible for protecting the public and upholding the law," District Attorney Rachael Rollins said in a statement.
"The community's relationship with members of law enforcement relies on trust, and actions like these harm the ability of every member of law enforcement to effectively perform their vital duties."