On Sunday morning, the force announced that the letters were being sent out after incidents at the Wren's Nest estate in Dudley and said: "Any further antisocial behaviour will not be tolerated and we will escalate our action if required."
It comes after fire crews trying to fight arson incidents on a housing estate in the area were pelted with objects by gangs.
On Saturday, police announced that they were enforcing a dispersal order in the area after a number of recent gang incidents.
The force said that groups had been lighting fires and then throwing things at crews from West Midlands Fire Service as they responded, and the order gives police officers the power to ban anyone for 48 hours from an area.
The order will be in place until noon on Monday and covers the whole estate, including the nearby nature reserve and Mons Hill, and spreads from Sedgley Road, along Birmingham New Road and onto the Broadway.
A spokesman for Dudley Police said: "A dispersal order, under Section 35 of the Anti-Social Behaviour, Crime and Policing Act 2014 has been authorised in the below area in response to groups lighting fires, throwing things at West Midlands Fire Service when responding and more.
"This behaviour will not be tolerated."