The clue behind the door

[Lisa]

No: HPFGUIDX 110223

As the elves pointed out this morning, the Do Not Disturb sign has 
come down off the door at JKR's website, and there's an interesting 
clue inside.

I won't post the clue here, as I'm sure some would like to check it 
all out themselves. Could this be a hint to the identity of the Half 
Blood Prince himself? There's someone in canon who bears an uncanny 
resemblance in my mind's eye to the note here.....

Lisa, ever pondersome