You can notify priority of serving by showing a notification on KOT. Use below script to print RUNNING on KOT for orders taken from already served tables.

Add below lines on top of the resource Script.SendOrder

if(ticket.getProperty("RUNNING")==null)
{
	ticket.setProperty("RUNNING","1")
}
else
{
	ticket.setProperty("RUNNING","2")
}

Use below script in all Printer.KOT resources to print RUNNING alert on top.

#if($ticket.getProperty("RUNNING")=="2")
	<line size="1">
		<text length="48" align="center" inverted="true" bold="true">RUNNING</text>
	</line>
#end