There must be a million of these signs all around Singapore. It's for the safety of occupants of buildings all over. That in case of any emergencies, the fire engine is able to park and the civil defence will take over.
They really go to the extreme here. Where they are these signs, the grounds have been "reinforced" where it will be able to withstand the weight of the fire engine. Shall spare you all the details.
Talking about Fire Engines, when you were growing up in your country you are reading this, do you have visits to Fire Stations? When you get to climb around the fire engines :-)
Terminology, if you are from elsewhere, Fire Engine = Fire Trucks.