Landships II

It certainly looks more like a Char 1a than anything else around at the time  - except that the Char 1a (FCM-1A) shouldn't have been around as late as 1921 (but who knows?). The uniform is interesting as being like nothing like anything documented as being around at the time.  Of course the film emusion may be fooling us but it looks very light in colour. The cut is more or less British but the headgear is outre (but looks 'tankerish'). The 'dedication' or whatever (which looks as if it is standing in a gents urinal!) has an American like signature (it would be unusual for Brits to sign an informal  note and include their middle initial) so it could be someone from the USA army doing "the grand tour". I think you've given us a mystery.