The memorial tribute, which features an image of Marshall and an anti-violence message, has been mounted in the footpath outside the hotel.
The personal message reads: "My name is Andy Marshall. On 8 May 2011, 29 years of age, my life was ripped away.
"An act of senseless violence that has no place in this world.
"It's a matter of choice. Treat others the way you want to be treated. Love is the greatest power of all."
Marshall's death in 2011 came as a cruel blow to extended family reeling from the high profile murder of cousin Guy just months earlier.
The pair had grown up together and Marshall had spent time working on the Guy family farm.
More than $4,110 was raised by the west Australian community to foot the bill for the plaque, spearheaded by the lead investigating detective.
Alan Marshall told the Herald on Sunday it was about leaving a legacy to honour his son and trying to salvage something good out of senseless act of violence.
"We wanted to reinforce that message around non-violence and the impact of bad decisions and how it affects so many people.
"It really is that ripple effect that goes out and keeps going out and the repercussions and consequences are devastating on so many people."
Marshall said they wanted to challenge the culture of violence.
"It's just to say senseless violence is unacceptable and there's a better way to live."
He said the sentiments on the plaque were what his late son "would have said and thought".