The right answer is the first one: No one is permitted to put seals on things in the possession of another, although he alleges that they are his or that they are pledged to him. This is stated in Book 2, Title 16.2.
The Code of Justinian was primarily a collection of laws, legal interpretations, and opinions of Roman jurists that emperor Justinian I sponsored between the years 529 and 565 with the goal of clarifying and updating the material and made the law more accessible and understandable - he, nevertheless, also added new laws. A committee edited the original laws and writings, but it is not possible to know to what extent. The Code became the only corpus of laws, and reference to other laws was strictly prohibited.
It consisted of four books. Book 2, where the above mentioned passage appears, is known as Pandects or Digest, a compilation of brief writings (mostly opinions but also extracts from treatises) by famous Roman jurists. Title 16, "That no one shall be permitted, without authority of the judge, to place signs (seals) on any property held by another," refers to the custom of placing seals to claim a possession. Justinian's jurists selected opinions from Emperors Probus, Diocletian, and Maximian that confirmed this law.