// get an incident that refers to a printer
var gr = new GlideRecord('incident');
gr.addQuery('u_serial_number', '!=','' );
gr.query();
gr.next();
var sys_id = gr.sys_id;

// print the raw value of the reference column u_serial_number
gs.info( "1. " + gr.u_serial_number ); // "1. 004f47b1db90e014023fe66505961913"
gs.info( "1a. " + gr.u_serial_number.toString() ); // "1a. 004f47b1db90e014023fe66505961913"

// print the display value of the same column
gs.info( "2. " + gr.getDisplayValue('u_serial_number') ); // "2. Lexmark CX860dte"