In dictionary, ‘Tauqee’ gives the meaning of signature or seal of a letter.
In Shia terminology, it denotes letters signed by Imam Mahdi. Some of them are Imam’s own writings, and some others are Imam’s dictation and written by his reliable companions.
During the two difficult periods of minor and major concealment, direct contact with Hazrat Mahdi (a.t.f.s.) has not been possible. A few of Imam’s companions would convey his message to people via the ‘Tauqee’.
For instance, the trustworthy Shaikh Abu-Amr Amri (p.b.u.h.) says:
Ibn-Abi-Ghanem Qazvini and a group of Shias debated and disputed over Imam Askari’s successor. Ibn-Abi-Ghanem said: ‘Abu-Muhammad (Imam Askari) has departed this world and has no successor. Later on, they wrote a letter in this regard and mentioned therein their differences. They sent the letter to the holy place. They received reply to their letter in Imam Mahdi’s handwriting as follows:
In the Name of Allah, the Compassionate, the Merciful
“May Allah protect you and us from conspiracies, and bestow you and us with the spirit of faith and certitude. May He safeguard us from a bad and evil end! Verily, news has come to me about a group who has doubt and uncertainty in religion and we have been informed of their doubt concerning their Master in the affairs. Therefore, we have become sorrowful, for you and not for ourselves and our condition have turned unpleasant for your sake and not for ourselves; since, God is on our side and so we do not need anybody, and we do not care anyone turning back from us! We have been created by Allah and after us; all creations have been created from us.” 
Here, we observe how Imam (a.t.f.s) has emphasized about the legitimacy of his Imamate and succession.
Another example belongs to the recent century where a ‘Tauqee’ was issued for Sayyed Abul-Hasan Esfahani, and delivered via Shaikh Muhammad Shariat Shushtari as follows:
“Inform him: ‘Lower yourself before the people (i.e., all the people should have access to you). Your place of sitting should be the entrance of your home, and you should fulfill the people’s needs; we shall assist you.”
The proof that such ‘Tauqee’ belongs to Hazrat Mahdi (a.t.f.s.) is the reliability and trustworthiness of the deputies and the narrators of ‘Tauqee’. All scholars and contemporaries have confirmed on their trustworthiness.
The narrator of the first ‘Tauqee’ is“Abu-Amr Uthman-ibn-Saeed Amri” . About him, you may refer to ‘Kalemat’ul Imam Mahdi’ page 139; and regarding the second narrator,“Sayyed Abul-Hasan Esfahani” , you may refer to page 559 of the same book.
Another reason to believe that such ‘Tauqee’ has come from Hazrat Mahdi (a.t.f.s.) is the predictions that have come down in some of them.
For example, Shaikh Kulaini has narrated from Qasim-ibn-Alaa as follows:
“I wrote three letters to Hazrat Baqiyatullah (a.t.f.s.) about my needs and informed him that I am an aged man having no children. Hazrat (a.t.f.s.) replied about my needs but did not mention anything about children. In my fourth letter to him, I requested him to pray to God to offer me a child. Hazrat (a.t.f.s.) replied me and he put down my wish as follows:
“O Allah! Grant him a son so that he may rejoice and make the current pregnancy of his wife a son!”
“I received the letter of Hazrat (a.t.f.s.) but I was unaware of my wife’s pregnancy. I went to home and inquired her about that matter. She explained that her problem is over. After some time, she delivered a son.”
This tradition has also been narrated by Hemyari.
Ali-ibn-Husain-ibn-Babewai met Husain-ibn-Rouh and set forth certain queries. Thereafter, he wrote a letter and dispatched it to Husain-ibn-Rouh via Ali-ibn-Jafar-ibn-Aswad. He requested Husain-ibn-Rouh to deliver that letter (wherein he had expressed his desire of having a child) to Hazrat Mahdi (a.t.f.s.).
In reply, Hazrat (a.t.f.s.) wrote:
“We have prayed to Allah for you in this matter. Soon you would be blessed with two beneficent and righteous sons.”
Thereafter, Abu-Jafar and Abu-Abdullah were born. Abu-Abdullah Husain-ibn-Obaidullah says: I heard Abu-Jafar (Shaikh Saduq) saying, ‘I was born by blessings and prayers of Hazrat Mahdi (a.t.f.s.), and he considered that an honour and glory.
Abu-Ghalib Ahmad-ibn-Muhammad-ibn-Sulaiman Zurari said:
Some time ago, I wrote a letter to Hazrat (a.t.f.s.) requesting him to accept from me a piece of land (as gift). My intention was not for gaining proximity to the Almighty Allah, but wished to associate with the ‘Naubakhtis’ and thus come on par with them in worldly ranks. I didn’t receive any reply. I insisted and repeated my request. Hazrat wrote:
“Appoint someone whom you trust and register you land in his name because you would fall in need of it.”
Thereafter, I registered this land in the name of Abul-Qasim Musa-ibn-Hasan Zajuzji, cousin of Abu-Jafar. I was confident in him and was aware about the magnitude of his honesty and belongings.
After a while, when the Bedouins took me captive and plundered my property and took away about my cattle and belongings worth a thousand dinar. I was taken captive for some time. Then I released myself by paying one hundred dinar and one thousand five hundred dirham. Besides, they took from me approximately five hundred dirham as a fee for the agents who accompanied me. When I became completely free, I felt in need of that land and then sold it.
In all those instances, we see Imam’s predictions have turned true and so the authenticity of ‘Tauqee’ is well established.