Holmes's "patriotic" V.R. done in bullets on the wall is visible in some shots.
The picture on the wall near the door in Holmes and Watson's living room depicts Major-General Charles George Gordon (nicknamed Chinese Gordon), who was killed in the Siege of Khartoum in 1885. At the time of Homes and Watson, this would have been a well known image in England.
When Watson first arrives at Baker Street, Holmes says "If this remains blue, all is well. If it turns red, it's a man's life" and places one drop of liquid on a piece of blue paper. He is clearly using Litmus paper to check whether the liquid is acidic or not. The paper would remain blue if the liquid were alkali or neutral (like water), but in this case, it turns pink, indicating that acid is present.
This episode makes reference to Holmes's cocaine use.