An authentic Holmes pin would be awesome. A cliche with bad accents not so much. To give it focus, it might be worth choosing an actor and style, with all the plot and art package that goes with it. Jeremy Brett, Basil Rathbone, Benedict Cumberbatch etc. There's plenty of material - no fictional character has had more movies made about them than Holmes, or for a longer time period.
Or go for an original licence-free approach e.g. steampunk Victorian kick-ass Holmes. Or would that be Houdini 2?