U will need to obtain a permit from Singapore Police Force. Upon
your return, you will need to show the permit to the Immigration
& Checkpoints Authority officers (more commonly known by public
as Customs) stationed at the Airport for their clearance. If you do
not have clearance from SPF and is found to
bring in such items, you might be detained and hand over to
SPF for investigations. Anyway you will have
to inform the airlines when you bring those items on board
anyway.