Signs used in the LRH
To form the Sign of Osiris Slain, simply extend your arms straight out to both sides as if you were forming the letter 'T' with your body.
For the Sign of the Morning of Isis, there are two versions you may choose from. The original version is created by simply putting your right arm up at a 90 degree angle to your left arm which is straight out to your left side (where it was in the previous sign), thus forming a letter 'L' with your arms. To create the second version of this sign instead (if you prefer), then you'll have to look into the thelemic works of Crowley. It's too difficult to describe the sign here without a picture. His version of this sign is one of the few things by him that I don't mind.
To form the Sign of Apophis and Typhon, raise the arms at an angle of 60 degrees to each other above the head, which is thrown back.
To form the Sign of Osiris Risen, cross the arms on the breast and bow the head.