A William Gillette postcard

I recently purchased this postcard of William Gillette on eBay. I knew nothing else about the postcard, but wanted to have a picture of Gillette dressed as Sherlock Holmes, and this image was an extremely common one. In fact, it's the image used on the Wikipedia page for Gillette (https://en.wikipedia.org/wiki/William_Gillette).

The postcard. The white text at the bottom of the photograph says "William Gillette" at center, and "Rotary Photo Co Ltd...". In handwriting at the bottom right of the postcard is "28/9/03 WJG". That translates to the 28th September 1903, and I should point out that Gillette's middle name was Hooker, and the initials WJG are not William Gillette's.

What I did not expect based on the description was that the reverse side of the postcard is addressed at stamped:

Reverse side of postcard. At left the message reads "Hope you are quite well to-day. W.J.G." and at right it is address to "Madame Sharrah, 55 Spring Bank, Hull". Hull is a city in East Yorkshire. 

The stamp and postmark. Consistent with other information on the postcard, it is stamped "3 PM SP 28 03" and "YORK". 

Well the initials WJG are enigmatic, and all I know is that the postcard was mailed from somewhere in Yorkshire to Hull (in Yorkshire). 

Who was Madame Sharrah? Thanks to the Friends of Hull Cemetery website (friendsofhullgeneralcemetery.com/inspirational-women) I have a little information Madame Sharrah (full name Mary Alice Sharrah) lived from 1863-1940 and was a music, drama and theatre teacher. "For teaching purposes she kept her maiden name of Sharrah, and referred to herself as ‘Madame Sharrah’. As well as music, she also taught drama and elocution, instructing many local talents such as Annie Croft, her son David Croft of Dad’s Army etc, Doris White and many others... lived at their large house at 55 Spring Bank, which still exists".

I'm interested in how common these Gillette postcards were. Gillette began a sold-out 216-performance run at London's Lyceum Theatre in September 1901 (www.gillettecastlefriends.org/a-gillette-timeline) but I can find no evidence that Gillette performed in York in the UK during or prior to 1903. Perhaps the postcard was brought back from London, or perhaps it was available for sale across the UK given Gillette's (and Sherlock's) fame. The postcard appears to be of trifling importance as a message, but was clearly valued enough by Madame Sharrah to be retained, and it survives to this day.