By the shaking of hands
1 THERE are two kinds of beings in heaven, namely: Angels, who are resurrected personages, having bodies of flesh and bones— 2 For instance, Jesus said: Handle me and see, for a spirit hath not flesh and bones, as ye see me have. 3 Secondly: the spirits of just men made perfect, they who are not resurrected, but inherit the same glory. 4 When a messenger comes saying he has a message from God, offer him your hand and request him to shake hands with you. 5 If he be an angel he will do so, and you will feel his hand. 6 If he be the spirit of a just man made perfect he will come in his glory; for that is the only way he can appear— 7 Ask him to shake hands with you, but he will not move, because it is contrary to the order of heaven for a just man to deceive; but he will still deliver his message. 8 If it be the devil as an angel of light, when you ask him to shake hands he will offer you his hand, and you will not feel anything; you may therefore detect him. 9 These are three grand keys whereby you may know whether any administration is from God.
 By the color of his hair
"There have also been ministering angels in the Church which were of Satan appearing as an angel of light. A sister in the state of New York had a vision, who said it was told her that if she would go to a certain place in the woods, an angel would appear to her. She went at the appointed time, and saw a glorious personage descending, arrayed in white, with sandy colored hair; he commenced and told her to fear God, and said that her husband was called to do great things, but that he must not go more than one hundred miles from home, or he would not return; whereas God had called him to go to the ends of the earth, and he has since been more than one thousand miles from home, and is yet alive. Many true things were spoken by this personage, and many things that were false. How, it may be asked, was this known to be a bad angel? By the color of his hair; that is one of the signs that he can be known by, and by his contradicting a former revelation." - History of the Church, volume 4, chapter 33