demonic possession

Compulsive sinning against your will: Addictions, uncontrollable anger, lust, urges to murder or commit suicide, etc.
Mental torment: Fear, depression, irrational heaviness in the soul, hearing voices in the mind, hearing auditable voices that nobody else hears, compulsive thoughts, insanity, mental illness, etc. Obsessive irrational worry is almost always a demon. People who are scared stiff over the unpardonable sin are in need of counseling and likely deliverance.
Emotional problems: Unable to get close to other people, sensing rejection for no reason, irrational emotional breakdowns, etc. Often more then just casting out demons is needed in this category, inner healing must also take place as well as tearing down strongholds.
Physical health problems: Arthritis, cancer, HIV, and a host of other illnesses are almost always caused by evil spirits. If it cannot be easily cured, then it's almost always a spirit that is causing it.
Occult powers or abilities: Anybody who can tell a fort