1) "ISH PLONI ED"
OPINIONS: The Gemara quotes the Mishnah in Gitin (87b) which says that if a witness signs "Ish Ploni Ed," his signature is valid. What exactly is the case? What type of document is the witness signing?
(a) The ARUCH HA'SHULCHAN (EH 130:7) explains that the enactments of the Chachamim regarding how witnesses should sign their names developed through three stages. Originally, witnesses were not required to write their actual names at all when they signed a document; they would write merely, "Ani Ploni Ed" (see Rashi to Gitin 36a). Beis Din could verify the signature of the witness only by investigating who the witness was and comparing his handwriting on this document to his handwriting on other documents. Later, Raban Gamliel decreed that a witness must sign his actual name, and not just "Ploni," in order to have more clarity (Gitin ibid.). This meant that the witness had the option to sign his name and his father's name, only his name, or only his father's name. The Mishnah in Gitin of "Ish Ploni Ed" was the third enactment, after Raban Gamliel's enactment. The Chachamim required that a witness write his name, his father's name, and the word "Ed." (See REMA EH 130:11 with regard to the Halachah in a case where the witness did not adhere to this requirement.)
(b) The Aruch ha'Shulchan (EH 130:9) adds that some understand that the opinion of the TUR (EH 130) is that prior to the enactment of Raban Gamliel, a witness used to sign his real name, but only his first name. Accordingly, the decree of Raban Gamliel must have been that a witness must sign his father's name as well. This understanding of the word "Ploni" is more consistent with the usual meaning of the word "Ploni" as it is used throughout Shas; the word "Ploni" represents any given name and not a specific name "Ploni."
However, the Aruch ha'Shulchan writes that this explanation is not plausible. The Mishnah in Gitin quoted by the Gemara here states that "Ish Ploni Ed" is a valid signature, but according to this explanation, after the enactment of Raban Gamliel a witness was required to sign the name of his father as well. The Aruch ha'Shulchan says that the only way to understand this explanation is to say that the Mishnah was stated before the enactment of Raban Gamliel. The Aruch ha'Shulchan says that he indeed found this answer in the LECHEM MISHNEH (Hilchos Edus 4:20).
The Aruch ha'Shulchan concludes that this explanation is problematic in light of many Gemaras (including the Gemara here) which imply that even the signature of a witness' name without his father's name is valid. (Y. MONTROSE)
2) THE SIGNATURES OF THE AMORA'IM
OPINIONS: The Gemara relates that a number of Amora'im did not sign their names at all when they were witnesses. They merely sketched an image or wrote a letter which they used as a symbol for their name. Rav sketched a fish, Rebbi Chanina a date palm, Rav Chisda wrote the letter "Samech," and Rebbi Hoshiya wrote the letter "Ayin." Is there any significance in these particular pictures or letters which the Amora'im used as their signatures?
(a) The RASHBAM (DH Rav Tziyer) writes that anyone who attempts to give any deep reason for why Rav and Rebbi Chanina drew pictures of a fish and a date palm is mistaken. The Rashbam apparently understands that Rav drew a picture of a fish because he was accustomed to eating fish, and Rebbi Chanina drew a picture of a date palm because he used to eat dates.
This explanation is difficult to understand. It does not seem logical that great Tzadikim such as these Amora'im would identify themselves in terms of the mundane world of the food they enjoyed.
The MAHARSHAL explains that the Rashbam does not mean that the Amora'im used as their signatures merely what they liked to eat. Rather, Rav identified himself with his special stringency to obtain large fish in honor of Shabbos, and Rebbi Chanina identified himself with his special stringency to have fine dates for Shabbos. The Maharshal apparently means that these Amora'im used as a symbol for their signatures the unique Mitzvah which they were especially careful to observe.
(b) Despite the caveat of the Rashbam, RAV YAKOV EMDEN in Gitin (36a) proposes a deeper reason for the pictures and letters used by the Amora'im as their signatures. He explains that Rav sketched a fish, because a fish represents a good omen. The Gemara earlier (118b) teaches that an Ayin ha'Ra has no power over a fish. Rebbi Chanina sketched a date palm, based on the verse, "Tzadik ka'Tamar Yifrach" -- "The Tzadik will blossom like a date palm" (Tehilim 92:13). Moreover, because Rebbi Chanina was in a position of rulership, he used the symbol of a date palm, the branches of which are fit to be used to hit (see Sukah 45a). This alludes to his awareness of his responsibility to lead the people in the proper path of Avodas Hash-m. Rav Chisda used the letter "Samech" to indicate that one may rely ("Somech") on his signature. Rebbi Hoshiya used the letter "Ayin" to symbolize the word "Ayin" -- "investigate"; Rebbi Hoshiya affixed his signature to a document only after he carefully investigated that the details in the document were accurate. (Y. MONTROSE)