I agree, we need some records that prove that we hold our stock in listed assets. When trading shares (that is real shares), I use an online broker who immediately generates a PDF when I make a purchase or sale. It usually has details such as; amount of shares I purchased/sold, amount in $, company, date/time etc. All the info you could need. I believe Bitfunder, BTC-TC and any other notable exchanges should have a somewhat similar system, so that a pdf of the trade could be provided under trade history or something. Again, I don't know how expensive or efficient it would be to set up something like that.