Anne-laure/Tony
Anne-laure Thats a good approach, and can be done other ways as well.
Your method would be what I would call a "hashtag based title link" reference. You could also just use [[book]] place these inside a comment <!-- #book -->, or just raw #book and use search or contains in a filter to find them (including hidden in comments), if you wanted as well, or you could have a tiddler-type field with the value "book". Except when hidden in comments, the new freelinks plugin will highlight book and #book if there is a tiddler called book.
The possibilities are infinite.
Regards
Tony