RAB-why not just sign?

[littleleahstill]

No: HPFGUIDX 136743

The writer of the note in the locket has three things to 
communicate: that s/he has the horcrux and means to destroy it; that 
s/he wants Voldemort to know that it is the writer who has 
discovered the horcrux secret; that s/he will be dead before 
Voldemort discovers what has happened.

That being so, there seems no good reason for the writer not to 
proudly sign their name, say 'Regulus Black'.  If, on the other 
hand, s/he wants to protect family etc from revenge in due course, 
why give any clue to identity, such as initials?  

Is there a reason for the initials, other than Ms Rowling having a 
bit of fun with us?   Are these initials which Voldemort will 
immediately recognise, rather than have to ponder 'er Regulus 
something Black?...something Amelia Bones'?  The other place we have 
seen initials used instead of names is in the labelling of 
prophecies- could it be there is another prophecy out there 
concerning Voldemort and RAB?

Leah