Gazelle's Calendar uses event icons to help you quickly identify different types of evens.
From the Screenshot Above:
Jim's Birthday - is a memo, indicated by the Sticky Note Icon
Alexis Stanwood - is a client appointment that is currently unconfirmed. Indicated by the Person Icon & Yellow Caution Icon
Dentist - Is a personal event, indicated by the Circle Icon
Kenneth Jones - Is a client appointment that is unconfirmed and inside the critical confirmation window, indicated by the Person Icon & Red Caution Icon.