Cognomina is the name of a secret society of people who possess total recall of their past lives. It is the plural form of a Latin word 'Cognomen' which means family name or in Roman times could mean a nickname. Members of this secret society, the Reincarnationists, take a cognomen or nickname when they are initially accepted into the Cognomina. That name is known only to each other and they use that name to identify themselves and others in the group when they come back in new incarnations.

As first described in The Reincarnationist Papers, members of the Cognomina all wear a black symbol tattooed on the back of their right hand between the thumb and the forefinger.
The members of the Cognomina call this symbol the Embe, and it is meant to represent the three peaks of the pyramids at Giza (two smaller pyramids over one larger one), where the first members of the Cognomina gathered to meet one another until the group moved to Switzerland.    
Some readers speculate that the mysterious tattoo has something to do with the symbolism of the Egyptian Flail.

The Reincarnationist Papers book includes a scene called the Ascension, in which new (or returning) Reincarnationists are asked to recall details from their previous lives. The expectation in this trial of sorts is for the initiate to provide enough detail from past live recall that facts can be verified to support the initiate's claims, at which point she or he is accepted into the Cognomina and they receive their Embe tattoo.

In The Reincarnationist Papers the members of the Cognomina meet and have permanent rooms in a mysterious hotel in Zurich, Switzerland. The hotel is called the St. Germain. Some people have had some fun researching the Cognomina, but that research is only available to readers who sign up for the reader club on the homepage

The Reincarnationist Papers says that there are 28 members, but that number may be larger now.