If you zero the USB drive out using `dd` or other equivalent tool that literally writes zeroes to each LBA, its safe. To avoid excessive wear and tear you can

If you zero the USB drive out using `dd` or other equivalent tool that literally writes zeroes to each LBA, its safe. To avoid excessive wear and tear you can really just get away with zeroing the first couple MBs - without a valid partition table or recognized file system, no OS will do anything when it's plugged in other than ask you to format it.