Props layouts are the base of most of features from Write The Signs. All other layouts are composed by a group of props layouts and regular props roughly saying, except Vehicles Layouts, once vehicles don't have props.

Field	Valid values	Description
saveName	free text	The name of the layout. Must be unique in the context (like in the city or in a Library).
propName	prop internal name	The prop used as base to write the stuff over
availability	RoadNodes Buildings PlaceOnNet	Define where this layout can be used
fixedColor	color RRGGBB	Color to paint the prop. May be overriden in other specific settings
fontName	installed font	The default font to use in this prop.

See Text Spot XML section. It can repeat multiple times, each one will become at least one text source in game, depending of their settings.