Reference
  TNC Settings

Header
A header line is pre-pended at the beginning of all formal and scratchpad messages to convey information to the FNpack program at the destination station. The header line is identified with the character string .hdr     The header may contain the following:

.aon - a request to sound an audible alert at the destination station
.pon - a request to print the message at the destination station
.dis - a request for the destination station to initate a disconnect when message transfer is complete
.ack - a request for the destination station operator to acknowledge receipt of the message.
The originating station operational callsign preceded by an underscore
The message subject preceded by an underscore

Trailer
An end-of-message string consisting of   $^   is appended to all formal and scratchpad messages. This string is used by the FNpack program at the destination station to mark the end of a message.   If the Add assigned callsign to message box is checked then the characters de followed by the FCC assigned callsign are also appended to formal and scratchpad messages.