Police have said they are investigating a complaint from a Sinn Fein MP about what he called "vile banners" on bonfires targeting veteran republican Bobby Storey, who died last month.
The news came as trouble flared for the third night in a row in north Belfast.
Sinn Fein MP Paul Maskey has complained to the police about what he called "a series of blatant and unacceptable displays of sectarian hatred on bonfires yet again".
"It is absolutely disgraceful that the grief of Mr Storey's family is being compounded by sectarian thugs," he said.
PSNI Superintendent Lorraine Dobson confirmed: "We are aware of imagery on social media platforms and we are making enquiries."
First Minister Arlene Foster said she had "regret" that some people did not abide by Covid-19 regulations at some bonfires and called on people to celebrate in a non-sectarian manner.
"They really need to take a look at themselves and ask themselves what sort of a Northern Ireland do they want to live in - do they want to live in a Northern Ireland where everyone is entitled to proudly celebrate their culture and identity, or do they want to live in a split Northern Ireland?" she told the BBC.
"I know certainly the one in which I want to live in, it's one where we can all proudly celebrate but do so in a way that is not offensive and certainly not sectarian."
Deputy First Minister Michelle O'Neill called the bonfire displays "anti-social" and said that more needs to be done to challenge them.
"Political unionism must do more to challenge and confront the destructive and toxic issue of anti-social bonfires," she said.
"These fires are not only detrimental to the environment, but also to community relations. Sectarianism has absolutely no place in our society and must be rooted out."
Meanwhile, a former SDLP election candidate who comes from a unionist background said she was dismayed to see her election poster appear on a bonfire.
"I feel I'm consistently very fair to the PUL community and the values they hold, so for my election poster to end up on a local bonfire feels really c***," said Heather Wilson, who grew up in the Ballysillan area. I intended to watch a local parade tomorrow, but not any more."
She received support from SDLP leader Colum Eastwood and UUP MLA Doug Beattie, who said the incident was "absolutely vile".
Meanwhile, firefighters responded to just 24 callouts to bonfires on the Eleventh Night - a fall of 29.5% on last year.
But the evening was marred by disorder in the mainly nationalist New Lodge area of north Belfast for a second consecutive night.
Superintendent Dobson said petrol bombs were thrown at police throughout the evening.
"As officers attempted to engage with youths in the area last night they came under attack from youths, some of whom were masked, who threw bottles and masonry. Damage has been caused to a number of our vehicles but, thankfully, none of our officers were injured."
And yesterday evening youths dragged sofas and furniture onto North Queen Street, where they torched them.
Earlier, it was reported that two males had been attacked in the car park of a Tesco store by a gang of teenagers from the New Lodge. The victims were thought to have entered the supermarket from the Tigers Bay area.
It is understood that one of the victims suffered a head injury and was taken to hospital by the PSNI.