The mark of a beast marks the trail (5)
I believe the answer is:
blaze
'the mark' is the definition.
(thesaurus)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for blaze that I've seen before include "Fire -- stripe on a horse's head" , "Conflagration" , "Vivid display" , "brilliant" , "rage" .)