A poster on the SF board asked what a barbeque smoke ring is. Looking for a good definition I came across this really great article about smoke rings, that pink color found around the edge of some slow-smoked meats.
It explains the chemical process going on, throwing around words like myoglobin and nitrosylhemochrome, but is understandable. It says
"When a smoke ring develops in barbecue meats it is not because smoke has penetrated and colored the muscle, but rather because gases in the smoke interact with the pigment myoglobin."
There can be smoke rings in products that are not smoked and a heavily smoked meat might not have a smoke ring.
I did have this perfect chicken once that was all smoke ring down to the bone. It was not only uber-delicious but a chick of beauty.
Pictures of smoke rings: