Icons can be associated with Leave types from Leave > Admin & Config menu, selecting a specific leave type, selecting an appropriate calendar icon and Saving your changes. The selected icon can then be used to indicate the type of leave requested. However, as it may not always be desirable to reveal the type of leave on calendars a configuration setting must be enabled to allow this.
From the Leave > Admin & Config menu, select General Settings and under Leave enable the "Reveal Request type when showing other employee requests" check box and click Save.
Once configured, the icons will now display on the Year at a Glance for the user in question, as well as in the Team Calendar, Calendar view.