I use the white fingernail polish and the black marker to indicate which side of the USB cable needs to be "up". Otherwise it's a pain to figure it out.
If you're male do be sure to tell the clerk at the makeup counter exactly why you are purchasing the white fingernail polish.
Also on black devices I will sometimes put white fingernail polish around the female plug just so I aim a bit better. Especially my Palm TX which as an large and complex connector.