$icon = Sprite.new
$icon.x, $icon.y = 600, 16
$icon.bitmap = RPG::Cache.icon(ICON_NAME)
Use that in a script call. Replace ICON_NAME with the filename of the icon. It needs to be written as a string, with quotation marks around it. For example, if your icon's filename was test. You would set the icon's bitmap like this:
$icon.bitmap = RPG::Cache.icon('test')
You need to use the the script call to dispose it when you no longer need it. Here is a safer method that won't crash the game if the icon has already been disposed.
if $icon != nil && !$icon.disposed?
$icon.dispose
end
The icon obviously has to be in your Graphics/Icons directory as well.
Hope that was helpful.