The process of transcribing a papyrus into a modern edition is known as transliteration. Papyrologists use a set of conventions to denote various features of the original, in order to present as much information as possible in a readable format.
Our online version of T. Gagos' "Select Bibliography of Papyrology" includes a list of conventions for the transliteration of papyri.
The first objective when transcribing a papyrus is to read the letters that are written on the papyrus. If a letter is damaged or partly missing, so that the reader is somehwat uncertain of what that letter is, then a dot is placed under the letter in the transcription. If letters are completely missing (if there is a hole or it is the edge of the fragment), then that part of the text is marked with square brackets.
Ancient scribes often made mistakes when copying texts, which they would correct in a variety of ways. Often, these corrections involved creatively transforming a wrong letter into the right letter. These sort of corrections can be difficult to transcribe. In other cases, the wrong letter or letters were crossed out and the correct letter(s) were inserted above the line.
In addition to the standard characters of the alphabet, ancient writers used a number of special symbols for a variety of purposes. Among the most common are the symbol for drachmas (a unit of money) and the symbol for "year", which was used when writing dates. Also, Christian texts often include a cross or chi-rho symbol. The Greeks also had special ways of representing numbers, dates and curency.