Read-only on Mac and PC
Assuming you have not already bought a suite of USB drives for this task, there are USB drives with hardware write-protect switches. It doesn't prevent anyone from flipping the switch back, but it sounds like you're not concerned about malicious intent, just making sure the editor(s) don't do something foolish.

This question has also been asked and answered on Super User. The accepted answer suggests that you should just set the contents of the drive Read Only. You could do this on one master drive, and then use something like Carbon Copy Cloner or Super Duper to replicate the data with the read only bits intact to multiple other devices.