You can find your unique reference code by; 

Mobile Application: Click the "Deposit" icon on the Home page > Choose between “Personal account” or “SRS account” > Then select "eGIRO or Manual Deposit" > Select “one time or monthly deposit” > Enter “the amount you want to transfer to your portfolio(s)” > Select “Your bank” > Under "Your reference code"

Web Application: Click on your "Name" on the top right navigation bar > Select "Settings" > Under "Reference code"