Police hope CCTV footage of a skateboarder falling off his board will help them find the "lowlife" who is believed to have earlier defaced a police memorial at Sydney's Domain.

Key points: Skateboard-carrying vandal seen scratching into wall on Friday

Skateboard-carrying vandal seen scratching into wall on Friday Crosses over names and abusive messages among markings on wall

Crosses over names and abusive messages among markings on wall Repairs might require deconstruction of wall

The NSW Police Force Wall of Remembrance was marked with scratches and abusive messages on Friday afternoon.

The wall displays the names of dozens of NSW Police officers who lost their lives on the job, and is the site of the state's annual National Police Remembrance Day service in September.

Police said the man believed to be responsible was recorded on CCTV skateboarding - and falling from his board - on nearby Prince Albert Road.

NSW Police Association president Scott Weber said the vandalism was a disgusting act that had horrified the police family and the public.

"How can some lowlife come here and actually desecrate a memorial to police heroes?" he said.

"What about the poor families? This brings up again those horrible days, those horrible incidents, the horrible weeks and years of a lost loved one.

"This is salt in the wounds for those families."

Police said the wall was damaged with a sharp object such as a rock or piece of glass. ( ABC News: David Spicer )

Detective Superintendent David Donohue, from Sydney City police, said a passerby saw a man scratching into the wall about 4:00pm on Friday.

He appeared to have used a piece of glass or a rock, he said.

"We look like we'll have to deconstruct this wall and have it professionally polished ... and that's something that really strikes at all the family members of the NSW Police Force," Detective Inspector Donohue said.

He said police had good DNA, fingerprint and CCTV evidence and were confident of making an arrest.

Police are investigating the vandalism. ( ABC News )

"Some of the CCTV footage we've obtained, we've observed him just near St Mary's Cathedral fall off his skateboard into oncoming traffic, and we're appealing to anyone who might remember that to make contact with police," he said.

NSW Police Legacy, which provides support to the partners and dependents of killed police officers, said the wall was a "special and reflective" site for many people.

"There are many families that will be certainly hurt by this vandalism," Legacy chairman Paul Bousfield said.

"It'll cause them immense pain, and we share that with them."

The vandal was described as between 18 and 23 years old, approx 178cm tall, thin, Caucasian, carrying a skateboard and walking "with a distinctive swagger", Detective Superintendent Donohue said.

"It's very difficult to tell whether he was affected by drugs or alcohol but I suggest no person in their right mind would go about doing this to such a sacred site," he said.