Ahh, the hat that is synonymous with Sherlock Holmes, even though Sir Arthur Conan Doyle never described the character to be wearing one... perhaps that's why in his latest incarnation, wonderfully portrayed by Robert Downy Jr, he [Sherlock] is wearing the bowler, since a rural hat on London streets would be a major fashion offence, but I digress...
The hat I have in mind is the 'Deerstalker' so called due to the fact that it was mostly worn by British gentlemen during outdoor activities such as hunting or ... deer stalking.
The brilliance of this hat is in it's unique signature design, the front and rear bill served to protect the face and neck, respectively, from sunburn, while the ear flaps tied up when not needed and tied down to protect from the cold. Checkered and twill patterns served as camouflage.
Back to the fashion savvy Holmes, indeed he would wear the Deerstalker hat, but in appropriate settings such as the country side or the woods or during a hunting outing. Never in the middle of London. The cartoon screen shot below is misleading, toon Holmes is committing major fashion faux pas but wearing that outfit on Baker Street.
At first glance the promo photograph below seems well styled, but no indeed, Holmes looks like he is going hunting and the fact that he is holding a magnifying glass makes him look ridiculous. The lady in the center and Watson are a bit mismatched as well but that is a whole other discussion... Let's stick to hats!