If I wanted to make a sign that links to save  id:12345  and says "My Save Here",  I would type  {c:12345|My Save Here}  in the contents of the sign. The vertical | thing (Unicode: U+01C0) is the Vertical Line Character, also known as a Pipe. 

The color of the text will turn to blue, and when clicked, the sign will open a save.

P.S.  Please check if your question has been answered elsewhere on the forum before starting a new thread.