This is based on signs which I’ve found in certain religions, cults, and movements, and everyone is free to contradict me.
1. Historical errors. A historical error can be as big as a belief in a major event which never occured, or as small as denying the existent of a certain group of people in history.
2. Culturalized truths. Culturalized truths are beliefs which have been taken from one or more cultures, usually to appease or appeal some people.
3. Hot drinks are bad. By this I mean hot and strong drinks like alcohol, hot coca, and coffee which are forbidden from being drunk, ever, not even allowed in moderation, because they are usually considered harmful to the person.
4. Evil is called good. This can range from evil being called good to evil being excused by an end (ends justify the means) to evil being covered up in good.
5. Brainwashing. Brainwashing in cults can take many forms: Only being allowed to get answers from the cult leaders, not being allowed to have non-cult friends, not permitted to - or at least discouraged from - asking questions, ignorance and misconceptions are spread as truth and reality to cult members, and being told to memorize or recite books without knowing what they mean or without being permitted to interpret them.
6. Defensive beliefs. Defensive beliefs means beliefs which are so conditional that they either deny the credibiliy of a non-cult person, they attack the scriptures of other religions by called them corrupted or incomplete, they accuse other religions of cospiracies regarding their teachings and scriptures, and they trick people into believing the cult beliefs - and examples of such tricks would include warm feelings, strange prayers, pseudoscience, half-truths used to lure people in, and new divine revelations (especially if those revelations are said to come from another religion’s god and the said god in said religion would never give the new revelations).
How would these signs mean a cult is from the demon? Because if it’s not God, than it must be from the devil.