I have recently taken to giving just a verbal warning, and then using only the Q lights for the standby and the go.
But, this is in a ballet, where often I have to call so many Qs in sequence that in order to give a verbal standby for the rail I would have to give it way early -- and then they get mad that they have to stand there holding the rope for that long. And most of the time its hard for them to hear me in the bitch box anyway. Using just a Q light, I can give the verbal warning 1 minute before the Q so they know to get over to the right rope, then I flip the Q light on in the middle of calling a lighting and deck sequence and when the rail needs to go at the end of the sequence I turn it off, and they go.
Also helps that we tend to have pretty much the same rail crew (or at least the same head flyman) for everything anyway, so they know how I work and know what to expect.
Just one way of doing it -- if you don't have a lot of Qs to call, then verbal standbys and gos are always helpful. Just make sure the rail has a good Q sheet to follow (what's on what lineset, Q light colors, speeds, etc).