In heraldry, a line which is drawn rayonny is made up of a series of flames. Not surprisingly it is often used to represent fire. While the use of rayonny is not a period practice, it is still allowed in SCA heralrdry.
Clarification: Rayonny is found occasionally in Italian heraldry at least as early as the 13th century, e.g. in arms on the the Sienese Biccherne, but it does not appear to have come into use in most heraldic styles until well after our period. -- Arval Benicoeur, Mar 2005