"It's a joke when [someone] steals a sign when you're wandering off to the pub. Well if he realises that affects his rates, maybe then it's a different scenario."
The amnesty will run until Friday, October 4, and anyone with signs is encouraged to drop them at Downer Whanganui at 501 Heads Rd.
People can also have their signs collected by calling Downer with location details.
Downer ran a similar amnesty in New Plymouth two years ago in which they collected any signs and returned them to their rightful owners.
Holmes said they have no database of signs to know exactly how many have been stolen over a period of time.
"You rely on the work crews to report signs that are missing, but what we don't know is have they been stolen or have they been lost?
"We just don't know. It depends on what they're actually reporting to their supervisor. It's the old story - if you lose things, you don't tend to report it."
Holmes also said stealing road signs could prove dangerous and costly.
"These signs are in place to advise and guide road users safely through roadworks. When they are taken, this places road users at risk.
"The cost of replacement signs is ever increasing, which ends up costing our community. Contractors don't have endless supplies sitting around."
If anyone sees someone stealing a road sign, they should call police, or if they see a sign in the wrong place, they should report it to the contractor it belongs to.