That exact herald appears on page 16 of Canadian National Steam Power by Clegg and Corley. It is described as a “pre-1919 advertising herald”. The diagram shows the evolution of the CN Herald. It indicates that the similar angled Canadian National logo was first applied in 1927. Sadly the GT logos aren’t covered by the diagram.
Since 6300 was built in 1927, perhaps the GT Railway System logo was tried on 6300, but was given up in favour of the simpler “Grand Trunk Western” on later locomotives. Since that is a builder’s photo, it is possible that the GT Railway System logo never appeared on a finish painted locomotive.
It reminds me of the paint samples Lionel had made up that are now prized by collectors as 'one-of-a-kind". This is like the “Lady Lionel” set of 1957 that was made with a pink locomotive and pastel colored freight cars. It probably sounded good on paper but in practice…not so much. [;)]