Carry SGD (Currency Notes less than $1500) in Check-In Baggage

Assuming this is accurate you're within customs limits but they might well have questions to ask anyway.
Add the danger of carrying that sort of cash and it isn't a good idea.

https://www.iatatravelcentre.com/sg-sin … etails.htm

Currency Import regulations:
Local currency (Singapore Dollar-SGD) and foreign currencies: no limit. However, amounts exceeding SGD 20,000.- (or equivalent)(incl. traveler cheque, bearer cheque, bill of exchange, promissory note) should be declared on arrival.

Currency Export regulations:
Local currency (Singapore Dollar-SGD) and foreign currencies: no limit. However, amounts exceeding SGD 20,000.- (or equivalent)(incl. traveler cheque, bearer cheque, bill of exchange, promissory note) should be declared on departure.

Better carry it otherwise, there is a slight chance you can lose it in your luggage.

Some baggers get something from our bags. It happened to me 4 times.

I lost shirts, chocolates, perfumes etc.

As for carrying the cash - hidden wallets

If carrying cash is better for you than ATM withdrawals, then you have the wrong ATM card - it's time to change!