STIR/SHAKEN (S/S) is a protocol used reduce spam phone calls by digitally signing originating calls. This means that when you're receiving a call, you can tell if it's a legitimate (signed) calling party number based on call display information. With S/S, you can more easily avoid spam calls and should see an overall reduction in fraudulent robocalls and illegal phone number spoofing.
S/S began to rollout holistically in Canada on November 30th, 2021. Since it's rolling out over time, not all calls will be signed at launch.