As several commenters have noted, Sound Transit is starting to visibly test their next train announcements. Oran shot the video above.
Testing is only occurring in isolated instances, and should be going on for the next month or two.
I hate to nitpick, but I’m not a huge fan of the scrolling — it’s possible to legibly encode a lot of information on a small board without doing so. [UPDATE- in the comments Sherwin says that the display will generally be static, with only intermittent scrolling.]