The graffiti aimed at actor James Nesbitt is being investigated as a hate crime.
The graffiti, which was written on a wall on Bushmills Road in Portrush, County Londonderry, mentioned the actor and was accompanied by a crosshair.
Politicians have slammed the letter, describing it as intimidation and a stifling attempt.
It comes weeks after Mr. Nesbitt spoke at a Dublin event about a united Ireland.
Gregory Campbell, a member of the Democratic Unionist Party, stated: “Jimmy Nesbitt is a native who has contributed to his community.
The member of Congress whose East Londonderry district was defaced with threatening graffiti demanded that the perpetrators cease their actions.
“Their actions are wrong and deserving of condemnation.
“I completely disagree with Mr. Nesbitt’s perspective regarding the future of Northern Ireland, but he has every right to voice his political views in any arena he chooses.”
‘Disgraceful’
Former First Minister of Northern Ireland Dame Arlene Foster wrote on Twitter, “I strongly condemn this attack on James Nesbitt, even if I completely disagree with him.”
East Londonderry Sinn Féin assembly member Caoimhe Archibald described the graffiti as a “sinister attempt to muzzle debate” and demanded that those responsible be held accountable.
Cara Hunter, who also represents the district for the SDLP, called the graffiti “totally appalling.”
“Everyone has the right to their ideas without fear or intimidation,” she continued.
The police suspect the graffiti was written on the wall between Tuesday at 17:00 BST and Wednesday at 19:30 BST.
They want to hear from anyone with knowledge of the event.
