Every customer has a 'Health Status' field in their profile. If there is anything in that field, it will be shown on the attendance taking screen once the customer has been marked as attending the class.
This is particularly helpful for Yoga classes, where it's important to know what poses your clients cannot do. Now the instructor can see any issues in that class at a glance.
The Health Concerns icon will show up next to the customer's name during attendance. You can hover over the icon to read the status:
You can set a health status for any of your customers by going to their customer Info tab, clicking the Edit Info, and entering the status in the Health Status field on the right side of the page.