For normal mail, there is no tracking number provided and in the case of lost mail, no compensation shall be claimed.
Below information is from Singpost website, https://www.singpost.com/delivery-solutions/registered-article/53-personal/send-documentparcel/422-registered-articles-faq.html
Q3: What is the difference between normal and registered mail?
Unlike normal mail, registered article service offers proof of delivery and limited tracking features. If an item is declared lost, we will provide compensation of up to S$68 per article or the declared value of the content, whichever is lower.
Q6: How do I know the status of my registered article itemitem? Is my Registered Article electronically tracked when delivered?