If you want to disable secure boot I THINK you need to:
1. Go to the Secure Boot menu in the BIOS (which I think is located in the Boot Configuration screen of the BIOS); and
2. Change the OS to "Other OS".
However if you want to hide the ROG logo during POST (and I am not sure why you want to do this ....) I think you need to:
1. Go to the Boot Configuration screen of the BIOS; and
2. Change Boot Logo Display to Disabled.
MOTHERBOARD: ASUS Maximus VI Formula (BIOS 0804)
CPU: Intel i5-4670k
HDD 1: Samsung SSD 250G 840BW EVO
HDD 2: Western Digital WD10EZEX 1TB Caviar Blue 7200rpm
RAM: 16gb (2x8) G. Skill RipJawsX DDR3-2133
PSU: Seasonic X-Series 750W 80 Plus Gold
GPU: Gigabyte GV-N770OC-4GD
CASE: Fractal Design Define R4
OPTICAL DRIVE: Pioneer BDR-209DBK
MONITOR: Samsung S24C300HL; BenQ E2200HD
OS: Windows 10 Professional
Other: MS Wired 600; Logitech MX 310; Sennheiser PC 151 & Logitech Z150