This splunk query will show information about USB mass storage device uses. You must be monitoring the registry using the Windows Technology Add-on (TA).

sourcetype=WinRegistry key_path="HKLM\\system\\controlset*\\enum\\usbstor\\*"  registry_type=CreateKey | eval Date=strftime(_time, "%Y/%m/%d %H:%M:%S") | rex "key_path.*usbstor\S(?<DeviceType>.*)&ven\S(?<Vendor>.*)&prod\S(?<Product>\S*)&rev\S"   | stats  count by Date, host, Vendor, Product, DeviceType   | fields  - count   | sort  - Date