In theory, at least, a full airep should be transmitted if the symbol is on a chart.
You can't rely on the 'M' symbol on the chart anymore. Both the Australian & NZ AIP state that AIREPS are not required anymore, due to the reports they receive from CPDLC equipped aircraft. The Fijian AIP seems to be silent on the matter, so I still report in that airspace. I can't comment on other parts of the world.