Frank's Clothes (Symbol)
When Chap lives at Cassiel's house, he needs clothes to wear, but Cassiel's old clothes are too small, so he takes some of Frank's clothes to wear. Frank, however, is the perpetrator of the crime, and by pretending to be Cassiel Chap is going along with Frank's plans and providing him with an alibi: how would Frank have killed Cassiel if Cassiel was still alive? While Cassiel is wearing Frank's clothes, he is tacitly agreeing to go along with the plan - clothing himself in Frank's deception, as it were. When he finally decides to go against Frank and confront him, he does so in Cassiel's old festival costume, discarding Frank's clothes and symbolically turning his back on his deception.
Hay on Fire (Motif)
The Hay on Fire festival, taking place in Cassiel's hometown of Hay-on-Wye, is a recurring element of significance. It serves as a vessel for the anticipation and climax of the story; chronological proximity to Hay on Fire denotes the level of plot-driven stress. It was the night of the festival that Cassiel delivered his frantic message to Floyd and was ultimately killed. Building up to the festival in the later year, the plot grows steadily more tense and complex before climaxing on the night of the festival, two years after Cassiel's disappearance. The final showdown tellingly occurs on the night of the festival.
The Wicker Man (Motif/Symbol)
The Wicker Man is the scarecrow-like figure on top of the bonfire at the Hay on Fire festival. It is revealed that Frank killed Cassiel by knocking him out with Helen's drugs and stuffing him into the Wicker Man, who burned when the fire grew. The Wicker Man then became a symbol for Frank's guilt and murderousness; later, when he's threatening Chap/Damiel, Frank says, "Shall I feed you to the Wicker Man too?" (Ch. 22). The scarecrow, innocent on its own, takes on the evil of Frank's actions and becomes a grotesque symbol.
Cassiel's Costume (Motif/Symbol)
When Cassiel disappeared on the night of Hay on Fire, he was wearing a black hooded cloak with a red-and-black mask obscuring his face, which was painted half gold and half silver. This costume conveys a sense of hiddenness and obscurity; when Cassiel wore it, it represented the hiddenness of his true life, that of the blackmailing jerk. The dramatic elements of the garb also reflect the dramatic climax of the events of the festival.
The symbol repeats in the course of the book; Chap wears the exact same costume at the festival two years later. In this case, the secret denoted by the hiddenness is the fact that Chap isn't actually Cassiel Roadnight. The dramatic climax also occurs on the same day, reflecting both symbolic meanings of the costume when Cassiel wore it.
Cassiel's Computer (Symbol)
Cassiel's computer is symbolic of his own fate. It appears that he himself erased its contents in preparation for his voluntary departure. Most people assumed that he had run away, and the evidence seemed to support it. However, there is a darker secret to both Cassiel's disappearance and his computer's tabula rasa. In actuality, Frank forcibly erased Cassiel's computer to make it look like the disappearance was voluntary, when in fact it was not. Cassiel's blank computer, then, symbolically represents his own volition (or lack thereof) in the outcome of his life.
