Broken Apple On Boot Up

Apologies if this has been discussed before, but...

Is anybody else getting a broken apple when booting in Mavericks ?

The bottom half of my screen shows a white screen with a broken grey apple covering the bottom half of the screen before the sequence moves onto the dark grey user login page.

Just wondering if it's a Mavericks quirk or the sign of something more serious ?

Cheers,

Paul.