For document executed before a Notary Public for use in a foreign country, the Foreign Agency may require that the authority and signature of the Notary Public be sent to the Singapore Academy of Law (SAL) for authentication.
If authentication by SAL, you should request the Notary Public to prepare a Notarial Certificate, in additon to the usual notarial services requirested.
If the Foregin Agency requires you to legalise (legalize) the document by the Foreign Embassy in Singapore, most likely, the authentication by SAL is required before you are able to send the document to the Foreign Embassy for legalisation (legalization).
At SAL, it will verify the authority and signature of the Singapore Notary Public and give a certificate to that effect. A fee is chargeable by SAL for issuing such Certificate.