This isn't evidence but a quick google search shows articles about the Perth one in June 21, and Cleveland in September 21.
Your googling is shite... When I search for "welcome to cleveland sign" (on duckduckgo) literally the first article shows you the story of the sign and its age: https://www.atlasobscura.com/places/welcome-to-cleveland-sign
The original is a "Welcome to Cleveland" sign near Milwaukee.
Cleveland, Ohio is also much scarier than Perth.
This isn't evidence but a quick google search shows articles about the Perth one in June 21, and Cleveland in September 21.
The Cleveland one has been up since 1978.
Your googling is shite... When I search for "welcome to cleveland sign" (on duckduckgo) literally the first article shows you the story of the sign and its age: https://www.atlasobscura.com/places/welcome-to-cleveland-sign