The Stirling Players theatre group had fixed a sign, which read �Kev�s Shed� in Fremantle Dockers colours, to the shed at its Morris Place, Innaloo property to honour former long-term member Kevan Hook.
Mr Hook was killed at 72 years old when a reversing bobcat hit him on the premises in 2011.
Theatre manager Elaine Morgan said members were �saddened� by what they believe was the theft of the sign.
�We do not know exactly when it went missing but one of our members discovered it gone about four weeks ago when they did a patrol of the grounds,� Ms Morgan said.
�We have not reported it to he police, it is just a sentimental thing for the members and Kevan�s family; we just hope it is returned.�
Ms Morgan said Mr Hook�s family agreed the sign was a �fitting tribute� to their hardworking relative.
When Mr Hook died, group secretary Carryn Mclean told the Stirling Times he was an �all-round great mate�.
Ms Mclean said he was appointed stage director in 2009, but he helped in other areas.
�He was a stickler for detail down to little details that sometimes a director may not have thought of,� she said.
�He was also a stickler for safety and was forever instructing anyone going on stage to be wearing the correct footwear when he was working on sets.
�He took great pride in his sets and rightly so.�
Ms Morgan said if anyone had any information about the missing sign, to call 9245 8683.
She is appealing to whoever has it to return it.