In North American railway traffic control, a "Form 19" or "31" train order would modify their schedule. An order which did not require a train to stop was called a "Y" (yellow) train order. The operator at the station would display a Yellow signal, which would cause the train to slow down so that they could receive the train order from a hoop from the operator. These commonly gave crews information about track speed (in areas where tracks and bridges needed repair) and were called "slow orders" by train crews. An "R" (red) order told the station operator to display a red (stop) signal, and dealt with meets, waits and other important traffic control issues, it was necessary for the crews to stop because they often had to sign for them, indicating that they had read and understood the situation. Orders were flagged at train stations by telegraph operators who signaled using a fixed "order board", which usually consisted of a single semaphore blade mounted over the operator's position in the station. The operator usually had to confirm to the dispatcher that the requested Y or R signal had been displayed properly before the dispatcher could issue further instructions to other trains or engines concerning that movement.