Reef pennants are often made of light three strand
line rove into the grommets with a stopper knot on each side of the sail. When you reef each pennant is tied with a reef knot around the bunt of the sail after bringing the new clew and tack down to the boom. I prefer to tie the pennants around just the bunt of the sail to minimize the chances of chafing and others tie it around both the bunt of the sail and the boom because they have bolt rope instead of slugs for the foot of the sail.
All the best,
Robert Gainer