Hi there, @awasser ...
This Guide provides the answer to the "U" that you see:
How do I use the Announcements Index Page? - Instructure Community - 1113 (canvaslms.com)
If you scroll about half-way down under the section "View Announcements", there are a couple bulleted items. The first bulleted item explains this:
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.
I hope this helps.
