Yeah if they allow a total stranger, 3rd-party entity like collective2 to autotrade your family member's account, how can they not allow a relative of your family member such as you to trade the account given proper authorization? LOL
What I am talking about is not theory. There is no way that brokers will freeze somebody's account just because it's been traded by someone else, unless it's unauthorized.
Your comment would have be interesting if you had said I just signed one with my wife and simultaneously with my mistress.
First off, if I trade an account that is under the same roof, even if a different IP address, there is no way the broker could ever prove who put on the trade! Maybe it would be a different story if the trade came in from a different locale...still better to be safe than sorry. It is only a broker form! Not a notarized anything! I have seen and signed the form electronically with Fidelity, why would they have that if they accept other crap! Ask yourself!
I still think the legal way POA is the way to go. You could trade your spouse or adult child's account without POA, not caught. But it is not legal. To broker, that is unauthorized trading since you trade someone's account without authorization with the broker.