FusionCharts PHP Class API lets you provide various chart messages while the chart is loading, retrieving data or rendering. For this you need to  use setChartMessage function.

 
To use setChartMessage put all chart message attributes and values in a delimiter (default is ;) separated string and pass to the function.
$FC->setChartMessage("ChartNoDataText=Chart Data not provided;PBarLoadingText=Please Wait.The chart is loading...");
 
To know more on the varous available chat message please see page: Changing chart messages .