Yup it should appear on a connected device even when not powered. For example in Linux:
[71844.486050] usb 1-4.3: new full-speed USB device number 17 using xhci_hcd
[71844.587198] usb 1-4.3: New USB device found, idVendor=067b, idProduct=2303, bcdDevice= 4.00
[71844.587212] usb 1-4.3: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[71844.587218] usb 1-4.3: Product: USB-Serial Controller D
[71844.587222] usb 1-4.3: Manufacturer: Prolific Technology Inc.
[71844.654783] usbcore: registered new interface driver pl2303
[71844.654791] usbserial: USB Serial support registered for pl2303
[71844.654803] pl2303 1-4.3:1.0: pl2303 converter detected
[71844.656068] usb 1-4.3: pl2303 converter now attached to ttyUSB0
Steve