The PSNI has launched an investigation after a picture of a snowman wielding a rocket launcher was daubed onto the front of a building that houses a support group from republican prisoners in Londonderry.
The picture was accompanied with the slogan 'Wishing you an explosive Christmas'.
The painting appeared on the front of Junior McDaid House in Chamberlain Street.
"We are currently investigating and assessing the matter," said the PSNI's Supt Gordon McCalmont.
Former DUP mayor of Londonderry, Alderman Drew Thompson said the painting suggested "violence remains on the agenda".