The second chapter of Maseches Kesubos opens with a Mishnah discussing a woman who was widowed or divorced and comes to collect her kesubah: "HaIshah shenisarmelah o shenisgarshah" - a woman who was widowed or divorced. A dispute arose between her and her former husband, who pays her kesubah, or between her and his heirs, who pay it out of the estate, regarding the amount of the kesubah. That amount depends on whether she married as a virgin or as a widow.
The claims of the two sides:
"Hi omeres: besulah nesasani" - the woman claims that he married her when she was a virgin, and therefore the kesubah due to her is two hundred zuz.
"V'hu omer: lo ki, ela almanah nesasich" - the husband, or his heirs, claim that she married him after she had already been married previously, and therefore her kesubah is only one hundred.
How is the matter clarified?
The Mishnah rules: "Im yesh edim sheyatzsah b'hinuma v'roshah parua - kesubasah masayim" - if there are witnesses that she went out in a hinuma and with her hair loose, her kesubah is two hundred. These two signs testify to the marriage of a virgin:
"Sheyatzsah b'hinuma" - the hinuma was a kind of veil that covered the bride's eyes, and it was used only for virgins.
"V'roshah parua" - her hair uncovered and spread over her shoulders, the way a woman who had not been married previously was brought out to the chuppah.
The Mishnah adds further: "Rabbi Yochanan ben Beroka omer: af chiluk kelayos re'ayah" - the distribution of roasted grain to the children at the wedding (parched grain that was customarily given as a sort of treat) is also proof, since this was done only at the wedding of a virgin and not at the wedding of a widow.
In summary: the burden of proof rests on the woman who is claiming the additional hundred zuz. If there are witnesses to one of these signs, we assume that she married as a virgin and she collects two hundred zuz; and if not, she receives only one hundred.