Reasoning: For a mention to work, the comment needs to contain a signature. This poses risks, as a wrongly formatted signature results in a mention not being sent. Therefore, we want to find cases of intended, but (for mentions) unsuccessfully made signatures.
Task: Look into the following cases and find out, with how much effort we could detect those errors and notify about them:
- message included signature not from self
- signature was embedded in template
- signature was not the same as ~~~ or ~~~~
Points to all cases are mentioned in https://www.mediawiki.org/wiki/Manual:Echo#Technical_details
Background: This task is based on a wish that received 21 points (#9) in the German Community Wishlist. Originally, the wish was to receive an information about the sent messages. To keep the number of notifications smaller, and to help people use mentions in a way that they are sent, the task informs about mention failures, and adds the reasons for the failure as well.
 Link to wish (in German): https://de.wikipedia.org/wiki/Wikipedia:Umfragen/Technische_W%C3%BCnsche_2015/Topw%C3%BCnsche#Bei_Speichern_Hinweis_.C3.BCber_abgegebene_Benachrichtigungen_.5BUmfrage_2015.5D
in English: https://meta.wikimedia.org/wiki/WMDE_Technical_Wishes#Notifications_about_failed_mentions