Hi Clint Anderson,
Thanks for contacting Syncfusion Support.
In our current implementation we do not have support for customizing SFAppointment icons and we have already logged a feature request regarding this and it will be available any of our upcoming release. Please check our website periodically to know the status of the features that are implemented.
Please let us know if you have any other queries.
Regards,
Rathanakumar S.