You focus yourself to draw from your shadow as ink, with a Calligraphy brush of a medium or finer size you can write a short 7 word message that any monk following the path of the Souls Shadow can read, alternatively any creature or being with truesight that can understand the language the message is written in is also able to read the message. 

To you and any creatures you designate when you cast the spell, the writing appears normal, written in your hand, and conveys whatever meaning you intended when you wrote the text. To all others, The script appears to be shadows that are being cast on the surface from the surrounding area. 

The message cannot be written onto any reflective or polished surface. 

A creature with truesight can read the hidden message.