The OP is probably just calling the isolated portion of a PCB the cold side. I see silk screen markings that clearly delineate the non isolated portion of a PCB when taking part DVD player power supplies. HOT is obviously non-isolated mains power, 'cold' would be the isolated side of the board, that side probably isn't marked cold but it's common linguistics to want to call it that.
and there are manufactrers that DO mark them HOT and COLD. as in "don't touch THIS ground, it's HOT, while that ground is COLD and it's ok to touch., and quite frankly, that is a good linguistic tool to keep us from touching exposed metal surfaces on the HOT side of a switching supply