When the character casts sepia snake sigil, a small symbol appears in the text of one written work such as a book, scroll, or map. When this symbol is read, the sepia snake springs into being and strikes at the nearest living creature (but does not attack the character). The target is entitled to a save to evade the snake’s strike. If it succeeds, the sepia snake dissipates in a flash of brown light accompanied by a puff of dun-colored smoke and a loud noise. If the target fails its save, it is engulfed in a shimmering amber field of force and immobilized until released, either at the character's command or when 1d4 days +1 day per caster level have elapsed.

While trapped in the amber field of force, the subject does not age, breathe, grow hungry, sleep, or regain spells. He is preserved in a state of suspended animation, unaware of his surroundings. He can be damaged by outside forces (and perhaps even killed), since the field provides him with no protection against physical injury. However, if he is reduced to –1 to –9 hit points, he does not lose hit points or stabilize until the spell ends.

The hidden sigil cannot be detected by normal observation, and detect magic reveals only that the entire text is magical. A dispel magic can remove the sigil. An erase spell destroys the entire page of text. Sepia snake sigil can be cast in combination with other spells that hide or garble text, such as secret page.