Format
A bull's format began with one line in tall elongated letters containing three elements: the Pope's name, the Papal title episcopus servus servorum Dei, meaning 'bishop, servant of the servants of God', and the few Latin words that constituted the incipit from which the bull would also take its name for record keeping purposes, but which might not be directly indicative of the bull's purpose.
The body of the text had no specific conventions for its formatting; it was often very simple in layout. The closing section consisted of a short datum, mentioning the place it was issued, the day of the month and the year of the pope's pontificate and signatures, near which was attached the seal.
For the most solemn bulls, the Pope would sign the document himself, in which case he used the formula Ego N. Catholicae Ecclesiae Episcopus (I, N., Bishop of the Catholic Church). Following the signature in this case would be an elaborate monogram, the signatures of any witnesses, and then the seal. Nowadays, a member of the Roman Curia signs the document on behalf of the Pope, usually the Cardinal Secretary of State, and thus the monogram is omitted.
Read more about this topic: Papal Bull