The SAL's MPs began in Richmond, VA and continue on today, even though the mainline has been removed in the region around the VA/NC border. The bottom photo shows that MPs also appear on signals, but not always. On former SAL lines and many others too, if a signal lacks a number plate, it indicates an absolute signal, i.e. a "stop and stay" signal.
Just followed a highway in Arizona using Google maps and streetview and found an example, looks like it's on both sides of the double tracks.
As seen in the darkness under the Central Ave. viaduct in downtown Atlanta on 04/11/1984 is the Western & Atlantic's "Zero Mile Post", set in place in 1842. Thankfully it's since been moved to a museum where it's safe and can be seen by all.
Mileposts around here in L&N country are measured from one point, Union Station in downtown Louisville. Mileposts can be on either side of the track from what I've seen, but usually next to the main when there's a siding. NS's Louisville District is measured from St. Louis, while their CNO&TP main is measured from Cincinnati. P&L is from Louisville to Paducah. The only real confusing one is CSX's CC Subdivision, as at Sinks, the mileposts change from KC to a "C" prefix, meaning the miles count from Louisville (over the now gone Lebanon Branch) instead of from Cincinnati. There's a bit of a mixup in that area that can be confusing if you're listening in on a scanner. Examples from railroads around here: CSX Q687, Sonora,KY 3/16/2021 by Jeff Wagoner, on Flickr CSX Q025, Trenton,KY 12/11/2019 by Jeff Wagoner, on Flickr NS 223, Waddy,KY 7/23/2016 by Jeff Wagoner, on Flickr RJC Z544-28, Winchester,KY 4/28/2022 by Jeff Wagoner, on Flickr I have noticed when out in Illinois that Union Pacific will have signs up for each quarter mile. UP 4014 North, Reynoldsville,IL 8/28/2021 by Jeff Wagoner, on Flickr
