warning: identifiers should not start with an underscore

I am writing a Pascal interface to an existing library (CarbonLib) that has underscores in some (only a few) of its symbol names. GPC issues a warning: identifiers should not start with an underscore. Before deciding to ignore the message or to change the name -- is there a special reason why identifiers should not start with underscores, except good use and general convention ? Regards, Adriaan van Os