Comment 3 for bug 1454657

Some suggestions on representation:
Bold font for the date, or
Keep the dot, but make it hollow (outline only) so as not to imply a relationship to a particular calendar
Change the background colour of the cell for the date that has an event or events
Implement a 'rising tide' effect where a shaded or gradient level rises from the bottom of the cell and it's height is greater depending on the number of events/amount of time scheduled that day.

The bold option is probably the most obvious/acceptable.