Read receipts are an optional feature that give you the ability to see and share when messages have been read. 'Read' will only be displayed underneath your most recent outgoing message if your contact has read the message and you both have the feature enabled. Long-press on a message bubble and select "Info" from the listed menu to see more message details.
To enable your read receipts on iOS
- Open Signal.
- Choose Settings .
- Choose Privacy.
- Tap on Read Receipts. It is enabled when you see a blue background and the slider is to the right.