Absolutely. If both the accounts are in your name, you will get a call from the compliance department and will need to submit a response (i've had a few accidents).
If not, you'd have people/funds driving up the volume on illiquid/thinly traded stocks for purposes of manipulation.
Exactly what the pump & dump scam is all about..they all have "family"
) they work the low volume pink-slip companies "stocks" created by their Nevada lawyers specifically for the pump & dump scam.
Professional silver tongued pump & dump salesmen rip unsuspecting investors off and walk away. The salesmen are usually owners of a couple million shares they own for less than a .01 anything above that pure profit....the latest versions are via cold calls to "traders"..they show the trader a little green profit...have him buy more & more then they "dump" in one or two days the stock falls back below .01
Now if you had a cousin/ close family member do it, i'm not quite sure how that works legally. I know for sure (not saying how) you CAN get away with it if you do it a handful of times a year. If it becomes a pattern, I'm sure that would be a different story. Technically if the legal entity is an arms length apart you really don't know where those orders are resting so the SEC would have a hard time trying to convict you until it became a trend.