On Robert J. Lang's Origami page is a very detailed article about diagramming and the commonly used symbols. It is really worth a read: http://www.langorigami.com/diagramming/diagramming.php
My preferred way to show repeat behind is a simple straight arrow with a line through it, pointing to the flap or point where the manoeuvre has to be repeated. If it has to be repeated on more than one flap, I make as many lines through the arrow as there are flaps. If a sequence that was several steps long has to be repeated I add the step numbers next to the arrow. Look at steps 23-25 of Gerwin Sturm's Tricycle diagrams to see what I mean: http://www.origami.at/diagrams/tricycle.pdf Personally I'm no friend of the single curve double head arrow for fold and unfold. Often-times it is important in which direction to fold and I can't seem to remember what the hollow and what the filled arrowhead means, especially since it often is not used in a consistent way throughout various authors. Therefore I prefer the two line one arrowhead arrows like shown in the same set of diagrams in step 5 for valley and step 1 for mountain folds. That's just my view on the topic and you are allowed to disagree. Nice Greetings Anna Kastlunger
