Does that put any shareholder in jeopardy if they turn out to only be holding markers instead of actual shares? Wouldn't the brokerage who gave them the marker be on the hook to provide shares should they want to sell? Sure would be a fine kettle of fish if one finally hit a major winner and then came to realize he didn't actually hold shares and may not profit as he expected from the investment assuming the worst case scenario that the brokerage went belly up due to a ton of outstanding naked markers.

Who would be the liable brokerage? The one who the customer placed his order with (say E*Trade) or the MM that E*Trade placed the order with?