Break signal is prescribed as a specification for ASYNC, and it is used when you would like the receiver to perform the operation different from usual data reception.

There are no rules in operation when Break signal is received. It is various according to devices, for example, switching the communication mode, performing forced termination of the process under execution, or ignoring completely.

However because of noise, it is possible that another data is seen to be Break signal as well as garbled characters of the regular data. Also, there are some devices of which the signal equivalent to Break signal might be output when turning on or off the power supply because of the hardware configuration.
On the OS such as Windows which supports plug and play, the OS itself may output the signal to the COM port when starting or stopping to confirm the device (such as the modem) connected to the COM port. At this time, it may include the state that the signal is seen to be Break signal by the device (including the analyzer) connected to the data.