1. The "No Photography" sign will be, in my view, an indication of a condition of entry to the building or shopping centre. Hence, if you wish to enter the shopping centre or stay in the shopping centre, you will need to abide by the "No Photography" sign.
If you then take out your camera and start taking photographs, you will then be in violation of the condition of entry, and the authorised buiiding personnel now has the right to ask you to leave.
If you leave at that point, then no harm done, and they can't ask you to do anything further, such as surrendering your camera, etc.
If you refuse to leave at that point, then you are now trespassing on their property. Trespass is both a criminal and civil offence, and they may use this as a bargaining chip to get you to do what they want. in other words "surrender your photos or I'll take action against you for trespass".
2. It is not illegal in Singapore per se, provided you don't fall under the usual upskirt/downblouse/outrage of modesty scenarios. By illegal, I mean a criminal offence.
It is also not "illegal (some people use this word to mean civil liability instead of criminal liability) in my opinion as far as civil liability goes. This is because there is no established cause of action which allows a subject to take civil action against a photographer.
There is no difference in terms of both civil and criminal liability as far as the subject is concerned, whether you are on the street or in a privately owned building. In the case of a privately owned building however, do take note of the trespass points I've made in (1) above. However, this is liability to the building management, and not the subject you are photographing (which honestly, has almost no right against a photographer).
In other words, if the subject complains to the building management and they find the complaint worth pursuing, they can ask you to leave or face trespass liability. However, as before, they have no right to ask you to surrender your camera or the like.
Two questions:
1. If you are in a building or shopping centre, "No photography" signs are common. Is this supported by Singapore law?
2. If you take a photo of someone (eg street photography), is it illegal in Singapore? And does it differ if you are on the street versus photographing in a privately-owned building?
Thanks.