What does the †† notation mean? I am reading a book on chess openings called 51 Chess Openings for Beginners by Bruce Albertson and the author uses notation like so:


  
  ...†† Kxf7
  


What does the †† mean? I know a single † means check however the author doesn't (to my knowledge) explain what the †† is meant to signify.

EDIT: here's a screenshot to provide some context of its usage
Well, after your update I come to the conclusion that these signs are used by the author to mark the omission of the notation of the respective move by White. 

This is not a common usage of them, and I have never seen it before. It should be documented somewhere at the beginning or end of the book. But I'd not be surprised  if it's not, since it doesn't reflect a healthy common sense to use the check symbol of all things for this purpose to begin with..