I've been able to find markers at a couple of properties.
What I try to do is first see if you see any signs of markers on adjoining
properties, or signs of obvious property lines. If you can find a "good"
marker that will help a lot as it will let you know how far back from
the road center line they were placing them.
As far as the pins themselves, that could be trickier if they are that old.
I'm not sure if they used rebar at the turn of the century. Maybe, but maybe
not. The suggestion of looking for rocks is a good one. In the old days,
rocks, and piles of rocks were often used as markers.
There may, or may not be a metal pin under the rocks.
If they used rocks, this may be noted on old plat maps, but again
maybe not..
Both of the properties I've found pins on used rebar as the pins.
This normally bangs a detector pretty good, so I would expect to find
them unless they have really sunk deep. In the cases I've seen so far,
they haven't really sunk much. I had no trouble detecting the pins with
my 250, and any of the coils.
At the TX property, the pins were along with no rocks. What clued me
to their locations was finding other peoples markers, and then noting
the setback from the road. Then it all fell in place..
At my OK place, pretty much ditto.. Once I found one good marker a
few lots down, I was able to note the setback, and it all started to fall
in place. I was then able to easily find my two front markers.
At the OK place, the pins were also of rebar, but they also had a pile
of rocks covering the pins.
I still need to find my two back pins, but I've been slacking lately..
I was up there this past weekend for about three days, but I spent
most of my time playing lawnmower man, vs tecting for pins..
Had a lot of mowing to do, and it kept me pretty busy.. My land was
in serious need of a haircut... :/ It's looks way mo better now..

I also took a new to me .22 rifle which I recently built up, and I had to
sight in the scope, etc.. So my spare time was usually popping that
thing, vs playing with the detector..
But.. I still intend to find my two back pins before too long.
I'm going to try it in the winter when the brush and grass is toast, and
it should be easier..
I think I've actually seen a pile of rocks at my N/W corner, but I forgot
where it was, and when I've tried to find it, couldn't.. But it was lush
and green, and that didn't help things. Should stick out better in
the winter.
BTW, when I was looking at a rebar pin at the TX place, I tried a
trick I had heard about using a compass to find pins..
IE: you take a good compass and run it along the ground where
you think the pin is.. If there is one, the needle will swing off a tad..
Well.. It works.. My compass could sense the metal in the ground,
and the needle swung a bit.

But the detector is still better and quicker..