How can I make scroll bars always visible?
When an activity that can be scrolled opened, the scroll bar should show for a few seconds before fading, therefore you can will know that the page can be scrolled. If you missed the subtle hint, then just slightly swipe the screen to display the scroll bar.

IMO, it wouldn't be a good idea to always display the scroll bar, as the scrollbar is in the content area and may obscure whatever is in the screen.