I'm not familiar with the laws in Singapore, but there would certainly be a few issues if you were to do the same thing in the United States.

• If a shop window is visible from a public roadway, sidewalk, or other publicly owned place, it is usually allowable to use any photos one takes from the public property. There are exceptions. For example, if the photo is primarily of a building or other intellectual property covered by trademarks or copyright, you might need permission from the owner of the trademark or copyright to publish a photo, depending on the usage. If the protected intellectual property is a small part of the background and not the primary subject or theme of the image, then you're much less likely to be liable for damages to the owner of the intellectual property represented in your image, regardless of usage.¹
• On the other hand, if the shop windows are only accessible from private property, such as a privately owned parking lot or inside a mall, then it is entirely up to the property owner whether to allow one to take photos at all, much less publish them. This is not a trademark/copyright issue, it is a property rights issue. The owners of private property have the right to determine what activities will or will not be allowed on their premises.
• Many malls in the united States have small signs posted at entrances to the effect that photography/videography on the premises requires the permission of the mall administrator. In such a case, one would need permission from the mall management just to shoot and be in the clear from a legal standpoint. This has been a longstanding practice which is becoming more and more unenforceable with the proliferation of phones and other very small devices with cameras.
• If the mall management or their representative observes one shooting and asks one to leave, remaining on the premises will constitute criminal trespassing. If they ask you to stop shooting and you continue, that could also constitute trespassing because you are continuing an activity that they have specifically prohibited.
• Even if you successfully complete your shoot and publish the results, the owners or management of the private property can request a court issue a cease and desist order regarding your use of the image or even sue you for damages. They might even have a case. But even if they don't, you're going to have to spend more money than it is probably worth to you to defend against their claim. You would still own the copyright to the image, but you might not have the right to publish/license the image for certain types of usage without permission of the property owner or their representatives.

¹ The classic example of this is the Transamerica building in San Francisco. A photo of the San Francisco skyline that includes the Transamerica Pyramid is not protected by the trademark of the building's appearance. This is because cityscapes are public domain. On the other hand, a photo that only shows the Transamerica Pyramid may be protected by the trademark and copyright held by the owners, depending on the actual usage of the image.