When you look at your shareholder certificates, there are different numbers there.  The SRN and HIN are ID codes for the purpose of identifying a shareholder.  What is the difference?

SRN = Security Reference Number
HIN = Holder Identification Number

aus.invest regular Tom N answered someone's question on the difference between SRNs and HINs, I've copied his  answer here because I thought it was a good summary. 

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SRN is issuer (i.e. the listed company) sponsored.  HIN is broker sponsored.

The practical differences: if you want to sell issuer sponsored shares, you can do it with any broker - you just need to supply theSRN.  If you want to sell broker sponsored shares, you need to do it through that broker or transfer the shares to another broker or to issuer sponsored (the original broker may? charge a fee for that).

Also changes to your portfolio of broker sponsored shares will show up on the broker's portfolio web page but issuer sponsored shares require you to enter changes yourself (at least is does on Commsec).

The SRN needs to be kept secret because with it and your surname and postcode, someone could get up to no good.

However if you have a free account at Link Market Services and Computershare (go to their websites to sign up), you will be able to see an automatically updated porfolio containing almost all ASX listed shares.  Some companies use small share registrars or don't use the full services of the brokers so they don't appear there.  e.g. STO and
BEN both use services provided by Computershare but not the full service so their shares don't show up in the automatic portfolio on the CPU website.  Another example, ISTR that JBM used some small WA registrar and WYL used to have their own in-house registrar.

BTW, it is well worth signing up for an account at Link Market Services and Computershare, because it makes it much easier to do things like change bank accounts for dividends, and some of the  paperwork sent by email instead.