I assume that top left is a generic topic, red means unread
bottom right is announcement? and bottom middle is info?
what do the other ones mean?

middle right is supposed to represent the animated one

Yes, this is the moved topic icon, I know it.ssilk wrote:When the moderator makes a link.
See for example:
https://forums.factorio.com/forum/vie ... f=6&t=8655
Currently can be also found in General: https://forums.factorio.com/forum/vie ... 5&start=75