Dave Rothgery found this article in the NY Times.
https://www.nytimes.com/2017/03/16/technology/personaltech/usb-drive-fat-windows-mac.html?smprod=nytcore-ipad&smid=nytcore-ipad-share
The Windows and Mac platforms have their own preferred file systems, but many external USB drives can work with both.
Make a Bootable OS X 10.9 USB Drive
" Here is another article from Ars Technica on how to make a bootable USB drive for Mavericks. This could come in handy sometime," Jim Hamm says.