We create a system-generated device name prefix consisting of 6 characters. We use a device name to reference devices that are provisioned to Esper. They are mapped to a GUID-based device ID we use at the API level. The device name is displayed on the Home screen of provisioned devices (noting it is possible to remove the device name for specific use cases).
If you are unhappy with the system-generated prefix, feel free to change it by going to Company Settings on your Console and then choose Edit Profile option, the company shortcode will be at the bottom. Find out more about Company Settings and the shortcode here.