Originally posted by musicbox:

Maybe we should check with the traffic police department about it. haha
I had the same question and wrote to LTA. Following was the reply:
Dear XXX,
VEHICLE LICENCE PLATE
FEEDBACK NUMBER: 328292
Thank you for your enquiry of 02-FEB-2006.
2. We wish to inform you that licence plates used for vehicles registered in Singapore should comply with the requirements specified in the Road Traffic (Motor Vehicles, Registration and Licensing) Rules. The vehicle licence plates must be so fixed that it remains easily distinguishable at all times. The vehicle licence plates must comply with our technical requirements and specifications such as colour schemes, height/width of characters, margins, typeface, etc.
3. Generally, we do not allow owners to affix the sticker type licence plates on their vehicles. We would only consider the use of such sticker-type licence plates if a vehicle does not have adequate space or a suitable location for affixing a conventional licence plate (i.e. those with base materials made of aluminium or acrylic).
4. If you require more specific advice on the use of sticker type licence plate on your vehicle, you may provide us with details (including pictures or photographs) on the size and colour scheme of the licence plate, and the proposed location of the licence plate to the Vehicle Engineering Division of LTA at 10 Sin Ming Drive, Singapore 575701.
Yours sincerely,
(SIGNED IN LOTUS NOTES)
LIM SAN TENG
ENGINEER (VEHICLE CONTROL SYSTEM)
VEHICLE ENGINEERING DIVISION
VEHICLE & TRANSIT LICENSING GROUP