SRN stands for Securityholder Reference Number. An SRN is used to identify the owner of shares that are held by a share registry (i.e. the shares are issuer sponsored).
Keep in mind
A HIN is different to an SRN. A HIN is used to identify the owner of shares that are held/managed (i.e. sponsored) by a broker like CommSec.
Your holding statement
The share registry will send you a holding statement with your SRN listed. If you can’t find a holding statement, contact your share registry to ask for one.
Search for "share registry" or look for help under Related Support.