They are referring to a #memorandum added to account #transfers, or discharges. I think you need a program to implement such transfers upon the steemit blockchain securely. The amount transferred and the accounts are still unencrypted, but the memo. is #encrypted for everyone but the two users or anyone with your private memo key.

You should be able to find your public and private memo keys under the Permissions tab of your Wallet tab, which you can find from your profile on steemit.com