That's not a metaphor for anything at all, Jamie Stewart will just trade you a comb and a sticker if you give him some of your precious locks, so that when he and his band return home from tour, they can light that hair on fire, and inhale it.
From a Xiu Xiu mailing list email:
During this tour, Xiu Xiu
will be giving away a special package (one per show) containing a Xiu
Xiu comb and sticker pack to the first person at every show who brings
them a lock of their hair taped to a card with their name on it. When
they return home from tour, they’ll make a video lighting each lock of
hair on fire while saying the persons name and inhaling the smoke [sic].
Via Electric Mustache, where you can go to read more about that, and also Jamie Stewart's blood t-shirts.