Google Maps lacks mile markers and the ability to toggle them in the view. You can see the mile marker if you zoom in on the map and drag down the peg guy in Street View.
If you need to find the mile marker, check the exit number near your destination. Frequently, exit numbers correspond to the miles where they are located. Find the exit number that is closest to the desired mile, then zoom in on the location and click on Street View. From there, using your mouse, pull down the peg guy that enables you to view a spot head-on. At this point, you must click the arrows that display in Street View to modify your perspective.
Depending on the arrow you select, clicking the arrows advances your view forward or backward. Zoom in on the mile marker signs as you pass them by using the arrows. On the majority of roadways, the mile markers increase as you drive north and decrease as you head south. After locating the initial mile marker, go north or south based on the mile number you wish to reach.