The Green Rider brooches are gold and depict a winged horse. They were forged by a man named Isbemic during the Long War for Lil and her Riders. It seems all Riders are people with innate magic, albeit only humble abilities, that can only be tapped when coupled with a Rider brooch. The brooch also identifies one as a Green Rider, but only to other Green Riders. The brooch is invisible or distorted to look like a simple trinket to the eyes of anyone other than a fellow rider. The brooches were originally forged during the time of the First Rider, and since then have been passed down to new Riders. New Riders are able to pick through all the brooches and choose the one he or she most identifies with, or feels most drawn to.
Laren Mapstone says that Rider brooches have "a way of coming back" whenever a Rider passes on. All of the modern riders possess a brooch that one of the original Riders wore. The connection between brooches can allow the ghostly spirit of another Rider to appear to the current Rider. Once, they were worn openly as a badge of office, but hatred for anything of a magical nature after the Long War pressed many to see that the brooches were destroyed. Instead, their maker Isbemic placed a spell of concealment on them, and perhaps as well as other traits, such as "calling" new Riders in, and also making it easier for magic to still exist and be utilized if the need arose without anyone being the wiser.
The brooches are usually cold to the touch, but seem to warm up whenever resonating with other magic around a Rider, such as wards or wild magic. The brooch will also not tolerate the touch of another, as demonstrated when F'ryan's ghost called to Karigan's brooch to burn Torne.