There is never just one comingling cockroach. You'll have to read the fine print of the TD Ameritrade agreement and then in light of the whole MF Global fiasco ask yourself if the hypothecation clause means anything if your shares get lent out or not. Who is to say they are not or would not be lent out if an arms length hedge fund asked to borrow your shares from the brokerage division. The only way to be sure is to either get the certs mailed out to you or put in an order on them.
It obviously works. We were up 13.7% today ; )
http://www.zerohedge.com/news/denials-begin-interactive-brokers-first-claim-it-has-not-engaged-commingling-rehypothecation