XMAS Challenge 3: Are they the Herts Imperial Yeomanry? and what is the event?

Xmas 2014 Challenge

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Obviously the mounted soldiers are waiting for something special (perhaps a royal visit?). The only clue is that someone has written "Herts I Y probably" on the back. If it is the Yeomanry the event was probably somewhere in Hertfordshire - in a place with a "RAILWAY COFFEE TAVERN"

Military

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So is it the Herts Yeomanry? Where is it? and when? The  back suggests about 1902/3 so might it be in connection with Edward VII coronation? And what is the significance of the stars and stripes? Perhaps the tavern owner was American? I will make a £5 donation for each key fact.

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