A law rune obtained in the Runespan is created by siphoning law esshounds and jumpers requiring 54 Runecrafting. This awards 54 and 107 experience respectively.
Law runes are worth 1.7 Runespan points and can be used to cross comet platforms. They can also be used to chip blood esswraiths. They will disappear and be converted into points if you leave the Runespan.
Players that try to bank any runes or essence from Runespan receive the message "A magical force prevents you from banking this item."