Your messages stay on “Sent” but never show “Delivered”
You stop seeing read receipts that you used to get
Calls to the person go straight to voicemail or fail repeatedly
Their profile photo, status, or “last seen” stops updating
You can no longer see their online activity
Messages to them appear to send normally, but they never respond
You are unable to add them to a group chat
Their contact appears differently or disappears in the app
Messages may still go through on some apps even if you are blocked, so none of these signs alone is definitive
The only sure way is to confirm through another communication method or ask them directly