CIC link says the following for Singapore
Do I need to provide a Police Certificate for Express Entry?
No. CIC will contact you after you apply for permanent residence. CIC will give you specific instructions and the information you need to get a police certificate. Please read the instructions below for more information.
Note: CIC will not accept police certificates sent by mail for Express Entry applications.
I guess so. They specifically mentioned that the SG police certificate will be required AFTER the PR application is made. So, If you have resided in another country/ countries besides Singapore, you will need to submit a police certificate from there. The Singapore certificate will be asked by CIC later during your application processing.
I am residing in SG myself, patiently waiting for an ITA.