Tom Jutilla, director of the Karpeles Manuscript Library in Tacoma, said he showed up for work Tuesday and discovered the plaque -- which bears the library's name and is believed to be made of bronze -- had been removed from its pedestal and apparently stolen, The Tacoma News Tribune reported Wednesday.
"It's very heavy," Jutilla said. "Whoever took it is not walking away with it very easily."
Jutilla estimated the sign's worth at about $4,000.
The library previously experienced a similar problem when members of the local American Legion post took one of the cannons from beside the building's entrance in an ownership dispute.
The dispute was resolved and the cannon was returned.
"We're going to have to start chaining things up around here," Jutilla said.