The son of slain police employee Curtis Cheng is still grieving his dad's death, while having to challenge those who would use it to justify bigotry.

The irony must have escaped them.

Not long after large posters celebrating Australia's long history of immigration were plastered up in cities across the country, a batch were defaced by vandals in Darwin.

Alpha Cheng says his family came to Australia to be part of the society. ( Supplied: Alpha Cheng )

But instead of the usual "f*** off we're full", a name appeared on the posters that would stop many passers-by in their tracks.

"RIP, Curtis Cheng was Aussie", they read, some with a white cross spray-painted over the face and head of early migrant Monga Khan.

On others, the words "real Australians say no" and "no PC" were smeared over portraits of others who travelled from overseas to make Australia their home.

It is a confused message — an anti-immigration outburst cum tribute to a murdered immigrant.

The irony has not been lost on Alpha Cheng, the son of the man fatally shot by 15-year-old Farhad Jabar outside Sydney's Parramatta police station in October last year.

"We came to Australia to be part of the society, my parents wanted me to get a good education," he said of his family's migration from Hong Kong.

"To see [my dad's name] as sort of a symbol of trying to exclude a certain group that looks a certain way from identifying as Australian, it's really sad."

It is not the first time Alpha has seen his family's tragedy played as a card against more recent arrivals, but he would like it to be the last.

An open letter to Senator Pauline Hanson

It was comments made by One Nation leader Pauline Hanson on the ABC's Q&A program earlier this year that first prompted Alpha to wade into the public debate.

In response to rhetorical questions posed by Senator Hanson about the causes behind Mr Cheng's killing and the Lindt cafe siege, Alpha wrote her an open letter, saying that he himself was still searching for answers.

Instead of 'welcome', the graffiti declares that 'real Aussies say no'.

But he described his "strong concerns" with One Nation's approach and stance and asked that his father's name not be used to promote fear and exclusion.

He went on to recount his own experience growing up as an Asian Australian in the 1990s, and the schoolyard abuse that he said was fuelled by hatred peddled by One Nation.

Two months after the open letter was published, Senator Hanson went on to repeat the reference to the Cheng family in her maiden speech to Parliament.

Speaking in the media and in the classroom

Alpha said he still didn't know if Senator Hanson has read his letter.

But the high school history teacher said he was considering reaching out to her again.

"Living in Canberra, it could be something that I'm looking towards, to maybe making contact with Senator Hanson," he said.

"It would be great to actually start a conversation because sometimes the best way to start to actually bridge understanding is to start a conversation and to listen to each other."

In the meantime, he is busy in his classroom teaching humanities and visiting other schools to talk about terrorism and extremism in a history elective.

The role of public peacemaker is not one Alpha said he expected to take on but said he had found himself in a unique position with something to say.

"It's something that I hope I'm able to give back, to help myself heal and hopefully even help society heal as well," he said.