Reference for Bava Batra 322:1
לאו דיעקב הוא
is not that of Jacob.<span class="x" onmousemove="('comment',' Hence no court would assume Jacob himself to be the witness. ');"><sup>1</sup></span> Is it not possible [that] be signed on behalf of his father?<span class="x" onmousemove="('comment',' Using the name of his father rather than his own, as a mark of respect. ');"><sup>2</sup></span> — No one gives up his own name and uses as his signature the name of his father. Might he not have used it<span class="x" onmousemove="('comment',' The name of his father. ');"><sup>3</sup></span> as a mere mark?<span class="x" onmousemove="('comment',' As an arbitrary combination of letters in lieu of his full name. Such a symbol or mark is as legitimate in deeds as one's proper signature. ');"><sup>4</sup></span>