To put it simply, they are runes used to, as it would be said,"To awaken a slumbering dragon.". Asleep? Why would he be sleeping in the first place? Well when a guardian dies, they go into a sleep state, as a spirit. Once they find a host in a human body, they usually are awaken. In some cases they shelter inside a human body and are still asleep.

"Huh? What is all this crap you are talking about?" you might ask. Can't tell you that unless you find out yourself. Research is a good tool sometimes. :P

For the sake of curiosity that people will have of who drew this,  elliey-sama is my ex, but drew it for me before we broke up.