What policies are in place to police financial speculation in the modern era?
I am afraid that "speculation" can be policed only very indirectly, since it is impossible to tell what "speculation" is and isn't. Look at Keynes' definition: speculation for the activity of forecasting the psychology of the market
In other words, you know the INTENTION of the speculator. You must see inside his head. I am not aware of any agreed-upon distinction of "enterprise" and "speculation," that can be perceived and judged objectively, from the outside. One activity can be speculation in one context and not in another.