What methods for identifying Sihr or magic have been outlined by the Ahlulbayt AS? Can signs like writing on walls, unexplained bruises, and persistent conflict in the home be considered clear indicators of Sihr?
None of the things mentioned in your question can be concrete evidence of Sihr or black magic etc. Ahlul Bayt (AS)'s teachings to avoid all types of Sihr, black magic and any harm is to recite Ayatul Kursi, Sura Falaq and Sura An Naas along with Sadaqa and Du'a. You then need not to worry about any thing as far as you are protected by these Quranic verses.
Wassalam.