Transmit for ID COMMS

The phrase "transmit for identification" means ATCATC —Air Traffic Control require you to say something so they can identify where you are (from the direction your radio waves approach them from, using VDFVDF —VHFVHF —Very High Frequency direction finding.) However, you are required to respond to the heading instruction, as this is a mandatory readback. Therefore, you can do two things at once by replying with the given heading. You do not need to ident unless ATCATC —Air Traffic Control specifically request you to do so.