Hi there
I had a very successful visit to TNA - looked at more than a dozen war diaries of Signals units and nearly 100 personal files of despatch riders. There's some fascinating information there, I'm still in the process of entering all the data into my database so I can work out what it all means!
The relevant diaries for the purpose of identifying the Indian Army unit in the photograph were WO 95/3919 Lahore Division Signal Company and WO 95/393 Meerut Division Signal Company. As I frequently found elsewhere, the recording by officers of similar units varied tremendously - some officers wrote long and detailed entries while others wrote the bare minimum.
The Lahore Division landed at Marseilles on 30th September 1914 and went by train to Toulouse, and thence by train to Argenton and Orleans where they were in camp from 2nd to 16th October. On 17th and 18th October they went by train to Boulogne, then Calais and St Omer. The stopping point for 17th and 18th October was written as BLENDECOUVES but I think must have been BLENDECQUES, which is a town near St Omer.
Over the following days they went by road to the Front through the following towns:
HALLINES; LYNDES; BAILLEUIL; ESTAIRES; LOCON; LEVANTIE; LE TOURET
In my opinion the photograph was probably taken in one of those destinations. I've looked at Blendecques and Estaires on Google StreetView and the architecture is very reminiscent of the photograph.
If the town survives, I think we have a good chance of identifying it - I expect the names of the shops will certainly have changed but it is quite distinctive with two four bay buildings looking onto a square with room for the Signals company and the photographer on the opposite side of the square. Have a look for yourself!
regards
Nick