I don't claim to be all-knowing so correct me if I'm wrong.

If its not specifically mentioned as any clause in your contract, typically the contract itself does not come into effect until you actually step into the office and begin your first day of work as there is no actual exchange of "consideration". Ergo, there is no employment contract in place. Of course, that doesn't stop the employer from suing you on civil grounds (which i doubt they will care)

Refer to this: ://.mom.gov.sg/faq/contract-of-service/if-a-new-employee-has-signed-a-letter-of-employment-but-does-not-show-up-for-work-what-can-an-employer-do

Of course, you can still be black-listed and what not, but i doubt any legal troubles will come your way.