The Lollipop seen on the cover of Carnival of Rust and more generally, its composition as a red and white spiral, is a common element in Poets of the Fall's iconography. The version on the album artwork uniquely features barbed wire for the handle.
The cover of Alchemy Vol. 1 features a symbolically analogous red ouroboros on a white background. The cover of Signs of Life features a monochrome red lollipop and the MV for False Kings features a red and white lollipop that does not form a spiral.
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CoR Album Art -
CoR MV Lollipop -
CoR MV Rollercoaster in the Mask -
CoR MV Targets -
LUtS MV Masks -
Ghostlight Album Art Wires -
Alchemy Vol. 1 Album Art -
SoL Album Art Lollipop -
False Kings Lollipop
Symbolism
Given the presence of of Yin and Yang on the cover of Signs of Life alongside a monochrome red lollipop in the opposite corner, the use of a spiral for the Carnival of Rust album's lollipop may relate to the second form of Taijitu - a two colour spiral, where the first form (Wuji) is undifferentiated and commonly depicted as a red circle. The second form sometimes features an empty circle at the center, which also fits with the CoR album artwork.
To complete the trilogy then, Temple of Thought would fit Taiji - the supreme polarity, represented by the two divergent angelic and demonic forms of Marko, in white and red respectively. To give weight to this assertion of the symbolism, Marko has a background in acupuncture and practices yoga, so he would have almost certainly come across these concepts from Chinese philosophy. The band is also known for utilizing traditional symbolism, such as with the Tarot cards or Commedia Dell'arte stock characters in the CoR MV or the Alchemical symbolism in the artwork for Alchemy Vol. 1.