Yes, I too have encountered a person or two at the Platinum line.
I simply point to the Platinum card and the Platinum sign...assuming that most people can make the association. Once or twice they still did not...but that was not my problem.
Of course this is a personal choice...but unless it is am emergency...I try not to use the Platinum line if there is only one person behind the desk.
I try to always make sure there are 2 or more....but again, that is not a requirement...just a personal choice.