A banner depicting a threat against former Sinn Fein president Gerry Adams is being investigated by police as a hate crime.
It appeared at the front railings of Belfast City Hall on Saturday.
A solicitor acting for Mr Adams said an image on the banner “can only be construed as a threat to kill and a hate crime”.
The PSNI and Belfast City Council are investigating.
Chief Inspector Gavin Kirkpatrick said: “Police received a report in relation to a banner that was erected on railings at Belfast City Hall at the weekend.
“Inquiries are ongoing into this matter, which was reported to police on Saturday and which is being investigated as a hate crime.”
In a statement Mr Adams said “there can be no place for hate crime or public threats”.
“The banner included an image of me under the title ‘Tick-Tock’.
“It also contained abusive and sectarian language underneath.
“The author/authors claim to have killed one person and clearly signal their intent to kill me.
“I believe the banner is a breach of the council’s by-laws and constitutes a hate crime and a threat to kill.”
Mr Adams said PSNI Chief Constable Simon Byrne has been asked to identify those behind the banner and asked whether inquiries have been made around securing any relevant CCTV footage.
“I have also written to Belfast City Council’s Legal & Civil Services about the display of the banner and making a formal complaint,” he said.
“The area in front of City Hall is monitored by CCTV and I have asked ‘what steps have been taken to secure the footage and any other available evidence… also confirm that you have or will notify the PSNI and co-operate fully insofar as securing any evidence which would assist in their investigation of a hate crime’.
“I have also asked if security officials at Belfast City Council will be monitoring the situation at future Saturday demonstrations at the entrance to Belfast City Hall to avoid the repetition of any further offence.
“There can be no place for hate crime or public threats. The PSNI has a responsibility to confront those responsible for such offences when they appear and to pursue those responsible through the courts.”
The council responded: “Belfast City Council has received correspondence regarding a banner which appeared on railings outside City Hall on Saturday February 6.
“We are currently investigating this matter and have made PSNI aware of the complaint.”