Turning the read receipts off won't let the user on the other side or the sender of a message know that you've seen their message. To turn off read receipts in Signal, follow the steps below -
1. Tap on the three vertical dots to open the menu of Signal.
2. Choose Settings.
3. Clicking on Settings will open up many options like Notifications, Appearance etc. Select Privacy out of all the options.
4. After selecting Privacy, a page similar to the below picture will open.
5. Scroll down the Privacy page and you will get to see the Read receipts option. Tap on the toggle switch to turn read receipts off.
Even though turning off read receipts is pretty useful in some use cases, but it also has its downside. If you disable the read receipts option, just like the sender of a message, you will also be not able to know whether the message you sent was opened or read by the recipient. But apart from that, it's a very nice feature added to Signal messenger.