[sigc] is possible make the emission of a signal private for a particular class?

[VinIPSmaker <vini ipsmaker gmail com>]

Hi guys, I was used to Qt, and I found libsigc++. Now I 
like much the flexibility of libsigc++, and I wanna know how can I make a
 behavior that is default and inflexible on Qt framework:

On Qt, if I
 have a class that emit signals, only the objects of this class can emit
 them, and anyone piece of code can only use the connect method of 
signals. How can I make this using libsigc++?