Internal read receipts
Read receipts give you the ability to see who has read your messages or comments within a shared conversation. You can access the list of recipients via the More menu of any message or comment.
NOTE On mobile, the More menu for comments can be opened by double tapping on any comment.
Can read receipts be disabled?
Read receipts are enabled by default. However, they can be individually disabled on a per-user basis for either messages or comments via the settings: Settings > Preferences > Appearance.