Decapitation of the Union

[RJNorton]

In his book John maintains that an inscription on a windowpane at McHenry House Hotel in Meadville, PA. was made by none other than John Wilkes Booth himself. John is certainly not the only author who has written that Booth did this. But did he? For example, here is what Roy Chamlee writes in his book:

Is this really Booth's work? Opinions?