Lee, I am not very familiar with its use but I believe M118 can be used for that purpose. You can also use the "echo" command in macros to sent messages to the console as he macros progress. No G code required and no parameters required. just add a line "echo "sending note to console"" and when it is read in the macro it will be sent. The following example is my current deployprobe.g file. Hope that helps.
M564 S0 ; let travel outside print zone if sensors.probes[0].value[0] == 0 ; if sensor is value ia 0 do this, 0 = probe attached echo "Probe already attached" if sensors.probes[0].value[0] == 1000 ; if sensor is 1000 do this, 1000 = probe detached G1 X53 F20000 ; X position of klicky dock G1 Y347 F20000 ; Y position of klicky dock M400 G1 Y175 F12000 ; slide out of dock return to bed Y center G1 X175 F12000 ; slide out of dock return to bed X center M400 ; wait for moves to finish if sensors.probes[0].value[0] == 1000 ;Check to see if probe is attached 1000 = not attached G1 X175 Y175 F10000 abort "Attach probe FAILED!" else echo "Attach Probe Successfull" M564 S1