As far as I know there are no proposals to redistribute wealth by seizing assets from wealthy people. They mostly revolve around increasing taxation.

Right now, when Bill Gates wants to use some of his wealth that is tied up in Microsoft stock, he has to sell it. When he sells it, he pays a capital gains tax of 15%. If we increase that tax, Bill gets less money and more of it goes to the government to be redistributed according to the wishes of the people (in theory!). There's no question of what the government is going to do with a bunch of stock.