A plaque was a sign noting an individual or event.
In 2365, Data, while masquerading on the holodeck as Sherlock Holmes, said to Katherine Pulaski and Geordi La Forge, "I saw the plaque 'The Home of the Red-Headed League' and this rope dangling from the bell, which enabled me to deduce that Mister Jabez Wilson was headed here to meet a most distasteful and untimely demise." (TNG: "Elementary, Dear Data")