When you have icons assigned to your Events you can choose to show or not show those icons when your Calendar is used as an Overlay. By default, when your Calendar Overlay will show all icons assigned to the Events in the source Calendar. However, if you don't want to show the Event icons from the source Calendar, you can choose the option to hide them in the Overlays management dialog.
Hiding your Overlay Event icons
You always have the option of returning to your Overlay management dialog and add your Event icons back to your Calendar Overlay.