With new 1.8 update, I see small exclamation points in all calendar events...why?

Just like the title said... Thunderbird updated, and so did Lightning (to 1.8), and now in all events I see an exclamation point in a grey box in the top right of all events, as well as some of them having another symbol I cannot make out (only showing up on Google calendar events, not on my other calendars not on Google).

I tried looking for release notes on 1.8 or some other explanation in the event creation dialog, but I was unable to find anything.....anyone know what these are about?

...or better yet, a link to the release notes that explain this change?  Thanks!