Hello @jmerriam ...

The "U" within the circle on your "Announcements" page does not mean that announcements are "Unread".  For whatever reason, that is the letter/icon that is used when announcements are imported from one course to another.  Per this Guide, How do I use the Announcements Index Page? - Canvas Community:

"A profile picture displaying the letter U in place of a user's profile picture indicates that an announcement was imported using a course copy, the Course Import Tool, or a blueprint course. Additionally, copied announcements do not include a posted date and time."

The blue dots that you see to the left of the check-box and "U" icon, however, are the indicators that those announcements are "Unread" by you.  I don't believe there is a way (at least not on this screen) to tell if a student has read an announcement.  You might be able to get an idea of which students are viewing your announcements by reviewing the individual access reports: How do I view the course access report for an indi... - Canvas Community.

Does this help to answer your question, Joan?  Let Community members know...thanks!  Take care...