By convention, we have chosen to "hang" the representation of the seals too - like it became common in Medieval times, but if our religion was greatly developed during this medieval period - the bible belongs to an earlier era: the Roman.The New Testament, which was written from the death of Jesus up to when it was compiled into an official collection in the 4th century under Constantine, thus, developed in the midst of that Roman world.
So it is in Rome of the first couple of centuries around the birth of Christ that we must look to understand the context, and what these seven seals represented for the faithful then. Also, what they would have actually looked like!
According to Suetonius, it was Emperor Nero who constituted laws concerning the procedure to properly seal documents. The translation of Suetonius' Latin text from the University of Chicago reads thus:
"It was in his [Nero's] reign that a protection against forgers was first devised, by having no tablets signed that were not bored with holes through which a cord was thrice passed."
It further elaborates that "The tablets consisted of three leaves, two of which were bound together and sealed. The contract was written twice, on the open leaf and on the closed ones. In cases of dispute the seals were broken in the presence of the signers and the two versions compared."
So we have words. And now we may proceed with actual pictures of what those words describe.
In order:
The first leaf was kept as record - but it would be the other two leave that concern us: The Diploma. This is showcased in the following pictures, where the closure was achieved by passing wire through the holes described by Suetonius.
Notice the holes on each leaf of the document through which wires would be passed. 
When the two leaves were closed onto each other, those holes were used to pass the wire that would hold it shut.
Then, a box was attached to contain the seals of the Seven Witnesses required for the document to be valid:
And finally, that little box around the seals, was itself closed with a lid to protect the integrity of the wax impressions left by the witnessing signets.
The point was to have the text of the document showing in full on one of the exterior plates. On the other exterior face, to the right and left of the seals-box were inscribed the names of the seven witnesses.
This way, the person in possession of the letters patent, could show them to authorities or whomever should be required to see them. In some ways, it functioned as a "green card" , visa, passport, etc. since for example - soldiers who after 25 years service were granted citizenship and received one of these letters-patent or "military diploma" would use them to settle in one of the provinces within the Empire and be required to register at the local Curia or Praetorian Prefecture [think Pontius Pilate in Judea if you decided to move there). Now, if the local authority thought the text had been altered or was in some way suspicious - he then would proceed to verify the unexposed text within the plates that faced each other and had remained sealed.
So breaking of the seals is an act which only a magistrate in reason of his judicial authority, could perform, and it was to verify that the external words still matched the internal, original, sealed text.
The seven seals guard the integrity of the contents as sealed by the seven witnesses. No sense in writing anything extra or adulterating the texts on the outside, when the judge will see the contents intact in due course! And woe to those who try! The message is not so complicated.
And all of these conventions had been imposed by Nero, right around the time of Christ... and its implementation would have been quite fresh in the conscience of those who wrote or read the bible in those first couple of centuries following.
So, seven seals: They didn't quite hang as later in the medieval charters, nor would the document have been a papyrus or leathery parchment scroll ... never mind a book out of paper! The Roman diplomas were made of metal.
Not a lot of them survive, though quite a few incomplete "military diplomas" are scattered around local museums in Europe.
The last two images above, to date and wit, are of the only extant specimen that conserves the seven seals intact. It remains, as it were, sealed, so we couldn't know if the text on the outside still matches the one inside. The original third leaf kept as a record by the offices of Emperor Vespasianus, who issued it, forever lost.
This diploma was found in Slavonski Brod some years back and not enough people know about it, so hopefully, now, more do!
