Carol and Dave Matthews installed the two-metre high 'Flame' sculpture in the garden of their Plenty home after losing their 22-year-old son Sam in the 2009 fires at their former St Andrews property.

It was stolen between Tuesday afternoon and early Wednesday morning.

The Matthews likened the theft to stealing their son's headstone and appealed for public help in finding their only physical reminder of him.

On Saturday morning, a passer by saw the sculpture in parkland on McDowell Street, Greensborough.

Greensborough police later returned the sculpture to the family.

Ms Matthews said the sculpture's return had restored her faith in people.

"Thank you everyone who took the time to help and share the Facebook posts," she said.

"Reading the comments many kind people left really helped us through a very painful time.

"I'm so thankful to the police, media and the many people who cared and restored my faith in people."

Sergeant Joanne Jamieson said police still wanted to hear from anyone with information about the theft.

"We're so happy that the Matthews have the sculpture back," Sergeant Jamieson said.

"However, we'd still like to speak to anyone who knows anything about the initial theft."

Police say it would have taken at least two people to lift the steel sculpture onto a ute or trailer.

Anyone with information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential crime report at www.crimestoppersvic.com.au