Aperture sights, often just called "peep sights" have been around on Marlin rifles both from the factory and as an aftermarket accessory for more than a century. These sights are, for many, the best alternative to optics and have proven themselves for generations in both target and hunting applications.
What are they?
Basically speaking, peep sights work through a theory called parallax suppression (for an excellent 23-page explanation of just what this is). The concept goes that the human eye will immediately jump out to and focus the front sight when looking through a very small, sometimes pinhole-sized, rear sight. The smaller the peephole, or aperture, the more it will force the shooter's pupil to focus.
These sights have been around since the time of the Civil War and hunters in the late 19th Century often used tang-mounted peep sights to take plains buffalo (bison) down at ranges out to a half mile with huge .45-70 and .45-100 rounds. At the same time, the practice of Schuetzen societies, in which polite city folk in silk and tweeds would gather to fire hyper-accurate target rifles at extreme distances or at tiny targets that simulated those same distances was very popular on the East Coast. Like the hunters, these recreational shooters used peep sights.
They proved so popular that most modern military rifles dating from the M1 Garand to the M14 and M16 use a small and often adjustable rear peep sight to help force the eye to the front post, making it more accurate.
Further, Marlin has a long history with these.
Over the years, many Marlins came equipped with rear peep sights as a standard. The Finnish Sako-based M322 of the 1950s (shown above), considered by many to be the company's best varmint rifle, came with a two position rear peep as the only option from the factory.
Likewise, the M2000 series benchrest rifles, Marlin's modern Schuetzen arm, came with big disk rear aperture sights. Other models, such as the M88/98 and the M1897 to name a few came with options for the gun could be special ordered with Marbles, Beeches, Osbourne or Lyman rear peep sights to make the gun hyper-accurate.
(The M1897 Bycycle gun with an optional tang peep sight)
Then of course, these companies, as well as others such as Redfield, have for decades offered aftermarket rear tang and receiver mounted options of various kinds
Today, as far as I can tell (please note in the comments below if I'm wrong), Remington-Marlin does not offer any peep sights as standard. Further, whereas older New Haven-made guns came pre-drilled with mounting holes on the left hand side of the receiver for these sights, newer Remlins do not.
However, just as in the past, there are any number of companies that offer peeps-- you may just have to drill and tap the holes. Then of course, there are models such as the Williams WGRS that mounts on top of the receiver taking the place of the rear sight mount. Our members have had good luck with several of these.
Williams peep sights to the Marlin 336c by forum member JB565
Another Williams on a Marlin 1895G by forum member Jstanfield103
Companies that offer these sights that are still in very active business today are Skinner, Lyman, XS, Talley, Brockman's (who even offer one with a Tritium insert in the front sight) and Williams. They range from $30-$230 depending on what you are getting and what you want to put it on and how much you shop around at Midway, Amazon, or Brownell's.
Try em, you may like what you see...