If it isn’t a configuration option then no. A workaround would be to use the Currency field type, which lets you replace the default currency symbol “$” with your own prefix so you can insert “S” at the start of your number. That won’t get you leading zeros, however. For that you would need a separate formula field that does something like: REPT(0, 4 - LEN({Number field}&"")) & {Number field}

We have created a form that allows you to mask the text in a field. It is a third-party form that integrates with Airtable.