I’m guessing the question is referring to one of these:

You may be thinking of a small clear tube that screws into the corner of the casket. It is located at the foot end of the casket, at the back, sort of where the left foot would be. It is at the very bottom of the casket, on the outside, and covered with a knurled metal knob, about 3/4 inch in diameter. It is sealed by a gasket against moisture getting into the tube.

This is a feature introduced by the Batesville casket company. They call it the “Memorial Record Tube.” I don’t know of any others that have copied them, but there could be some.

The purpose for this little tube is to hold a little slip of paper, about 1.5 x 6 inches, rolled up into a scroll. On this scroll, the Funeral Director would write identifying information so that the decedent, cemetery and funeral home could be identified without needing to open the casket looking for an ID band on the body.

You may have heard of severe flooding in places that washed out cemeteries, exposing caskets which then would be moved about by the flood waters. These caskets have to be identified so that they can be properly reburied.

This is the sort of thing the Memorial Record Tube is meant to address.

Some areas are not prone to this sort of problem, so some funeral directors do not take the time to fill it out. Also, a good number of cemeteries now attach a waterproof ID tag to the outside of the casket as the last step before lowering it into the grave. This serves the same purpose.

These devices are intended to store a slip of paper with the vital information of the person residing in the casket.

The purpose is so that in the event of a natural disaster or some other reason the casket is removed from its place of burial, there will be irrefutable proof of whom is inside of it.

This infographic (not created by me), illustrates exactly why these are built into caskets.

Image courtesy of Google

As you can see, without that slip of paper, there would be virtually NO way to properly identify the remains inside of the casket.