As of my last update, Facebook does not provide a feature or notification that informs users when someone has blocked them. However, there are a few signs that may suggest you've been blocked by someone on Facebook:
1. **Search for the Person's Profile**: Try searching for the person's profile using Facebook's search feature. If you can't find their profile in the search results, it's possible that they've blocked you. However, it's also possible that they've deactivated or deleted their account, or that their privacy settings prevent you from finding them in search results.
2. **Check Mutual Friends**: If you have mutual friends with the person you suspect has blocked you, you can ask one of those mutual friends to check if the person's profile is still visible to them. If the profile is visible to others but not to you, it may suggest that you've been blocked.
3. **Look for Previous Interactions**: If you've had previous interactions with the person on Facebook, such as comments on posts or messages in Messenger, check to see if those interactions still exist. If you can't find the interactions or if they appear to be deleted, it could indicate that you've been blocked. However, it's also possible that the person has deleted the interactions or left the conversation themselves.
4. **Try Mentioning or Tagging Them**: If you try to mention the person in a comment or tag them in a post and their name doesn't appear in the autocomplete suggestions, it could indicate that you've been blocked.
It's important to remember that these indicators are not definitive proof of being blocked, as there could be other reasons why you're unable to find or interact with someone on Facebook. Additionally, blocking is a private action, and Facebook does not notify users when they've been blocked by someone else. If you suspect that you've been blocked, it's best to respect the other person's decision and refrain from further attempts to contact them.