Heya! I have earlier answer about medieval identity theft and impersonation that talks about authenticating seals!

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I’m an English heir of a noble house whose been away for 10 years warring in the holy lands. When I come back, all my family has died, who do I have to prove to that I’m the legitimate successor and how would I go about this?

Have you been writing letters back home? Engage in any business before you left? You're in luck--but probably not for the reason you're thinking.

Any ID-issuing, record-keeping centralized office is a long ways off in the future. But the later Middle Ages did have a form of identification for nobles, high-ranking Church officials, and others who might have to engage in long-distance legal rulings or business transactions: the seal.

You would carry with you a lead seal matrix--basically, a stamp, that you would press into softened wax and attach to the letter or charter (here's a picture of a letter with the seal intact). The use of the seal would authenticate the document as yours, but even more so, in medieval thought it would actually stand in for your physical presence.

In other words: seals were really, really important in the Latin Middle Ages. Brigitte Bedos-Rezak, who wrote the groundbreaking article on this topic, argues that theologians start to theorize about the semiotics of seals around 1200, but the same ideas are present inchoately going back to around 1050.

So as long as there is a wax seal of yours somewhere back in Europe, you could demonstrate the identity of your seal matrix's imprint with the earlier one. Bedos-Rezak includes an example from the later 13th century that I think fits nicely as an illustration here. Although it concerns the authentication of a document rather than a person, it involves contested ownership of lands following the death of the owner.

A man named Renaud de Trit brought a charter to King Louis IX in which Louis granted some specific lands to him, as heir of the deceased countess. But unlike the above pictured example, this seal was broken and half of it was lost, leaving only “half the legs of the figure representing the King, and the stool on which his feet were resting.” Louis’ inner cohort (including the author here) agreed that they couldn’t be sure the charter was really his, and he could give the lands to whomever he wished.

But Louis called for a charter of his where the seal was unbroken, and told the gathered skeptics: “‘My lords, here is the seal I used before I went overseas, and you can clearly tell from looking at it that the impression on the broken seal corresponds exactly with that of the one that is whole. Therefore I could not, with a clear conscience, retain this land.’” (Jean de Joinville) And he restored Renaud’s inheritance to him.

You're probably wondering, "Well, what about forgery? What if I was the impostor who stole the seal off someone's dead body?" Before you jump to this as some backwards "Dark Ages" failure in the medieval system, consider fake IDs and digital identity theft today. And just like we do now, medieval people worried about forgery, too--a lot. It was a capital crime (death penalty), for starters! And the subject of very much wrangling, with no good conclusions, in canon and civil law. Conrad of Mure (late 13th century) eventually just declared than an authentic seal was one that was "well known and famous."

Beyond the theorists, there are stories about people faced with kidnapping who ditched their seals and rings (another form of identification, although less fraught than seals) so letters, charters, and other documents couldn't be forged by their captors.

So you've got a seal that is yours, or one you've taken off the dead body of the noble whose prospects back home seem much better than your own. Renault, in the above example, took his charter and his claim straight to the king and his council. But it was directly relevant in this case, since the lands in question were being held by Louis himself. In general, where you'd take your case depended on which (more or less) sovereign lord you ultimately answered to.

The Holy Roman Empire, with far more territory than any of its neighbors, was too large for a stationary nexus. The imperial court was "itinerant," that is, the king's whole household, retainers, and nascent bureaucracy perambulated around the Empire. If the emperor was in a convenient location to you, you could take your case to his bailiffs and court. Otherwise, German law tended to operate by principality, which in the twelfth century could mean a state, a city, the secular holdings of a monastery...the increase in written bodies of law from the thirteenth century helped streamline things a bit more.

Little England had the easiest time with consolidating some level of centralized oversight ("some" being...not very much, yet). From the mid-12th century, assize courts took over a lot of disputed land claim cases through local trials by jury; eventually, the 'mort d'ancestor' assize would be established to give jurisdiction and procedure specifically over land inheritance cases.

In France, the major innovations came under Philip Augustus. Preparing to leave for the Third Crusade, he and his regents/caretakers established (among other things) a legal system of traveling courts to take over for the king's itinerancy. Teams of two to three bailiffs rotated around the kingdom, setting up a court once a month to hea)r cases in whatever region they were in. Dissatisfied customers had the right to appeal to Parlement (and pay the treasury) in Paris. This system, like the others, endured long after the reigns of the kings under whom they evolved into being.

Now it's time to get some knightly retainers of your own, and go storm other lords' castles and burn their peasants' villages and show just how much of a holy warrior you are at heart.