gtk-tooltip-set-icon-from-icon-name (tooltip icon-name icon-size)

tooltip -- a gtk-tooltip object
icon-name -- a string with the icon name, or nil
icon-size -- a icon size of type gtk-icon-size

Sets the icon of the tooltip, which is in front of the text, to be the icon indicated by icon-name with the size indicated by icon-size. If icon-name is nil, the image will be hidden.