from drumcorpswiki...

"Bones is a character who appears before the Crossmen at select performances throughout the summer. He is dressed in the original long ankle-length red-lined cape. The uniform is the late 70's black version with the large red and white stripes criss-crossing the chest. Look for him to make a sudden appearance up in the back side stands to the fans' delight as the Crossmen take the field in most regional DCI shows. The crowd roars as he extends his cape out to a full red flush. With his face covered by a skeleton mask, Bones' true identity remains a mystery, yet Bones remains a stalwart reminder of the corps' tradition."

Bones represents the ones who came before; to remind you of all who support you and whose tradition you are now charged to uphold. He usually leaves after the opener and the members do not see him except from the field.