Earplugs are life saviours, especially during the drab, seemingly endless metro ride or to avoid those awkward hellos when you pass by someone you don't want to make conversation with. It is also one way to effectively filter out all the peripheral chatter and the cacophony of the everyday mundane, when you need to focus. Even night-time easy listening becomes 'easier' when you have a pair of earplugs for company.
The slightly upward jut of the ridges, helps identify the "L" earphone.