1998 Australian 5 Cent RDm Letter Is Peculiar

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I think "RDM" is for Raphael Maklouf who designed the effigy on the 5c coins from 85 to 98. I couldn't get a clear enough photo to enlarge to check though.

After spending a little I finally transferred the images.

Both images are of the 1998 Australian 5 cent but separate coins.

If you're referring to the "RDM", those are the designer's initials, as SallyG noted. You'll find those initials in that location on all the portraits of that design - on all denominations of Australian coins, and on the coins of every other country that used that portrait.

To the naked eye, the initials do somewhat resemble the word "POM", leading to an urban myth that some rabid anti-monarchist at the Mint put that there. But as can be clearly seen in your scope shots, the letters are indeed "RDM".

Sorry, only just noticed that.

This lettering is incuse, not relief, as I understand it. Which means that any kind of gunk or goo the coin is exposed to is likely to get stuck down there, and once something's in there, it's not coming out again easily. "Why just the M and not the other letters?" Well, you can see in your pic that is is indeed inside the other letters to a small extent. I'd suspect some kind of liquid (juice, coffee or some such) that spilled a bit there, most of it landed in the M but some in the other two letters too.