Witch Writing (Widdershins writing, left-handed writing)
Witch Writing creates a disguised piece of writing whose true message can only be read under certain circumstances.
The Netbook of Witches and Warlocks
By Timothy S. Brannan and The Netbook of Witches and Warlocks Team
You decide on what circumstances will reveal the true writing, and you also decide what the false writing is. Common choices for circumstances are as such: Script can only be read in normal moon light, can only be read on a full moon, the blood of a virgin or an innocent man must be dripped on the writing, a particular command word must be spoken, etc. You can affect a number of pages equal to your caster level.
At the end of the duration, both the true writing and the false writings become illegible, though you can re-cast the spell indefinitely.
The arcane focus for this spell are a special dual tipped writing pen (or quill), which is not consumed and a special ink of lemon juice and silver dust, about 30gp per page.