The Signs of which Allah, the Most Holy, the Most High, has spoken in the Holy Quran are The Imams (a.s.)

Al-Husayn ibn Muhammad has narrated from MuAlia ibn Muhammad from Ahmad ibn Muhammad ibn 'Abdallah from Ahmad ibn Hilal from 'Umayyah ibn Ali from Dawud al- Riqqi who has said that he asked Imam abu 'Abdallah (a.s.) about the meaning of the words of Allah in the following verse.

"The signs and warnings are of no avail to the disbelieving people." (10:101) The Imams (a.s.) said, "Signs are the Imams (a.s.) and warnings are the prophets (s.a.)."

H 534, Ch. 18, h 2

Ahmad ibn Mahran has narrated from 'Abd al-'Azim ibn 'Abdallah al-Hasani from Musa ibn Muhammad al-'Ijli from Yunus ibn Ya'qub (in a marfu' manner) that abu Ja'far (a.s.) has said about the words of Allah, the Most Holy, the Most High, ". . . but they rejected all Our signs. . ." (54:42) 'The signs are all the successors (of the prophets (s.a.)

H 535, Ch. 18, h 3

Muhammad ibn Yahya has narrated from Ahmad ibn Muhammad from Muhammad ibn abu 'Umayr or someone other than him from Muhammad ibn al-Fudayl from abu Hamzah who has that he said to abu Ja'far (a.s.), "May Allah take my soul in service for your cause, the Shi'a (your followers) ask about the meaning of the words of Allah, "Of what do they ask one another? (78:1).

Do they ask about the great news?"The Imams (a.s.) said, "It depends up on my decision. I may tell them or may not tell them. Then he said: "I like, however, to tell you the meaning thereof." 

I then asked what is the meaning of, "Of what do they ask one another?" The Imams (a.s.) said, "It means Amir al-Mu'minin (a.s.). Amir al-Mu'minin (a.s.) used to say, "None of the signs of Allah, the Most Holy, the Most High, is bigger than I and none of the news of Allah is greater than I."