If you are rimming your glass with sugar - pour a thin layer of heavy cream into a small, shallow plate. Pour the red sanding sugar out on a second small plate and spread it into an even layer at least as wide as the rim of your glass.
Place the martini glass upside down in the cream to coat the rim. Then, dip the rim into the sanding sugar. (You can use a spoon to help get the sugar onto the entire edge of the glass.)
Fill a cocktail shaker with ice. Pour in the crème de menthe, irish cream, and crème de cacao. Cover a shake vigorously for 30 seconds or until well chilled.
Strain into the rimmed martini glass and serve immediately.
Notes
The amount of cream and sugar needed to rim the glass will vary depending on the size of the plate used. I used a small saucer just wider that the glass rim.