I've been asked to find a few over the years, sometimes with success. At least in our neck of the woods there will be a few master markers that are usually made out of brass and are quite sizeable. Usually in a corner lot and all the others are referenced off this one. We have one in our yard. Most of the rest of the markers are 1/2 or 3/4 pipe, usually 18 inches or so long, pounded into the ground.
Basically you have to learn to listen for all the iron hits that you've trained your brain to ignore, or have discriminated out. And anybody that has detected for more that eleven minutes knows there are usually dozens of iron items in every square yard of turf. Sometimes if the marker is close to the surface you may get an overload signal that most nails and other doo dads aren't big enough to produce. It is best to get a lot map from your city. Once you find one marker you can use a tape measure and get a pretty good area where the others should be. If in fact they are there.
Chris