The grey chain icon, goes to the post or comment address on your instance.

The colored federation icon, goes to the home instance address of the community the post or comment is part of.

The left is a link to the post on the current instance, the right is a link to the post on the instance it was posted from.

These are from the inbox view, right? Let me know if you see them next to each other elsewhere.

The paperclip will take you to a “context view” of the reply. The fediverse icon takes you to the content on its native instance (which may or may not be your own).