A single * symbol on the top, what's that? how to play? with photo.

[formusic]

A single * on the top of piano music score, what's that? how to play? with photo.
Thanks.

[keyboardclass]

Usually there will be another asterix at the bottom of the page with a comment - otherwise I've never seen it before.  Is there a preface to the book? 

[formusic]

Thank you! May u send personal message, or leave your email. I will send the music score to u. Maybe you will know it.

[rmbarbosa]

In my edition of Chopin Nocturnes edited by Konemann Music Budapest, this * refers to the critical notes, usually available at a site. For example, in my edition * refers to www.Koenemann,com.where we may find theese critical notes. I think its your case.
Best wishes,
Rui