When a dragon bonds a rider, they give them their heartscale, which the rider must keep with them to solidify the bond. It's a mark of trust between dragon and rider, and must be protected at all costs. 
Dragon Keepers will wrap them with wire to help hold the scale tight, and some say the wire wrapping matches aspects of the aura of the rider. 
 
Choose the color of your dragon, or choose random to let your dragon choose you!