Watson takes Sherlock to meet with a potential sponsor in episode 1x08 "The Long Fuse".
A hooker leaves M's hotel room and then M preps for another murder in episode 1x12 "M.".
From episode 1x17 "Possibility Two".
A woman is pushed in front of a subway car in episode 1x18 "Déjà Vu All Over Again".
Sherlock summons Watson to the park to talk about the use of carrier pigeons in their current case in episode 2x01 "Step Nine".
Sherlock holds up a sign in front of CCTV cameras in the square to contact Langdale Pike in episode 2x01 "Step Nine".
Watson visits the grave of Gerald Castoro and encounters Joey Castoro there in episode 2x02 "Solve for X".
Detective Bell discovers a body in a chemical drum in episode 2x13 "All in the Family".
From episode 3x16 "For All You Know".
Watson questions a restaurant owner about two missing women in episode 4x01 "The Past Is Parent".