Οφείλω να προσθέσω και το χρήσιμο ιστορικό:
Similar to the school bells that most of us heard during our school days, the New York Stock Exchange's (NYSE) opening and closing bells mark the beginning and the end of each trading day. More specifically, the opening bell is rung at 9:30am EST to mark the start of the day's trading session. At 4pm the closing bell is rung and trading for the day stops. There are bells located in each of the four main sections of the NYSE that all ring at the same time once a button is pressed.
Interestingly enough, the signal to start and stop trading wasn't always a bell. The original signal was a gavel, but during the late 1800s, the NYSE decided to switch the gavel for a gong to signal the day's beginning and end. However, after the NYSE changed to its present location at 18 Broad Street in 1903, the gong was switched to the bell format that we see today.
A common sight today is the highly publicized events in which a celebrity or executive from a corporation stands behind the NYSE podium and pushes the button that signals the bells to ring. Many consider the act of ringing the bells to be quite an honor and a symbol of a lifetime of achievement. Furthermore, due to the amount of coverage that the opening/closing bells receive, many companies coordinate new product launches and other marketing-related events to start on the same day as when the company's representatives ring the bell. This daily tradition wasn't always this highly publicized either. In fact, it was only in 1995 that the NYSE began having special guests ring the bells on a regular basis. Prior to that, ringing the bells was usually the responsibility of the exchange's floor managers.