Bootable USB without an OS shows as Windows in Startup Manager I was going to do a clean install of El Capitan and I created a Bootable USB drive. After making the drive I done the usual, I restarted while I held down the option key to white I was presented a screen with startup disk option screen and predictably I found my usual HDD that my OS is on, my backup drive, and my bootable USB which is called "Windows".



That's weird since I've never installed Boot Camp on this machine.

When I boot from the "Windows" drive there's just a blank screen and the letter "J" flashing on it and nothing else happens. 



Just a "J" in the top left of the screen.

What is this?
Obviously something went wrong in making the bootable USB stick.
It should be 8GB.
Why not use a little tool that does it for you:
Diskmaker_X,  see http://diskmakerx.com
You have to have the OSX installer on your disk: if you already installed it and it is gone, download it again from the Purchased tab of AppStore.