I'm sorry, not everyone has 10 year old glass monitors. Some people upgrade them and have a LCD monitor. Putting tape/dotting your screen will damage the screens pixels most likely resulting in a few dead pixels on your screen[spots where nothing shows]
And most crosshairs don't really work unless you inject them into the game. A universal crosshair isn't really possible w\o them blinking just because most FPS's days now ds are full screen priority.