Sugar soap as typically found in Commonwealth countries is a cleaning material of variable composition sold for use on surfaces affected by greasy or tarry deposits which are not easily removed with routine domestic cleaning materials. When in dry powder form it looks like table sugar thus causing the name.
The precise ingredients and their proportions (and consequentially what hazards, if any, are associated) vary between manufacturers and suppliers but are now generally found listed in the Material Safety Data Sheets found on manufacturers' and suppliers' web sites. The alkali component is normally sodium carbonate or less commonly sodium hydroxide at a concentration of a few percent and an organic solvent and an abrasive agent are normally the other functional ingredients, as well as coloring and water. Many brands of sugar soap are freely available for domestic use in the UK, being commonly sold for preparing surfaces for redecoration, stripping certain types of wallpaper, removing accumulations of grease in kitchens or removal of tar deposits caused by tobacco-smoking; products are supplied in powder to be diluted before use or liquid form to be brushed or sprayed.
The comparable cleaning product in the USA is trisodium phosphate, also known as "TSP". However, due to environmental concerns about the impact of phosphorus on lakes and streams, products labeled TSP may not actually contain any trisodium phosphate.
A comparable product in France is sold under the brand name St Marc. It is branded by Reckitt Benckiser and its formula is a derivative of a resin soap made from terpene. The ingredients listed in the safety data sheet  include >30% sodium carbonate.