Is it permissible to declare a slain person a martyr if good signs appear on him?

The Shaykh : Is it permissible to testify that a mujahid is a martyr if karamat (miracles granted to a righteous person) appear after his martyrdom, such as a pleasant scent like musk emanating from him, or is that generally impossible?
If signs appear on a person slain in jihad, that is hoped for him, meaning these circumstances strengthen the likelihood that he is a martyr, whereas testifying to it is difficult.