If want to smuggle stuff, don't ever use a motorcycle. ICA staff would be on duty to check all bikes. That's why many traffickers kena caught when they used their bikes to bring small quantity of drugs into Singapore. For cars it would be the auxiliary cops. But even if your car escape the first check by these auxiliary officers and have your passport stamped by ICA officer , always remember the 2nd one is the most important as before u exit the Woodlands checkpoint gantry, ICA officers would always be around that area to do random checks on cars that they deemed suspicious.