What was Socrates' "divine sign"?

Most would say it was his conscience although it seems clear he saw it as more than just his own inner thought process and believed that 'god' had ordered him to speak the truth.
http://home.wlu.edu/~mahonj/Ancient_Philosophers/Apology2.htm
https://en.wikipedia.org/wiki/Apology_(Xenophon)

Another better explanation:

"Perhaps the most interesting facet of this is Socrates' reliance on what the Greeks called his "daemonic sign", an averting (apotreptikos) inner voice Socrates heard only when he was about to make a mistake. It was this sign that prevented Socrates from entering into politics. In the Phaedrus, we are told Socrates considered this to be a form of "divine madness", the sort of insanity that is a gift from the gods and gives us poetry, mysticism, love, and even philosophy itself. Alternately, the sign is often taken to be what we would call "intuition"; however, Socrates' characterization of the phenomenon as "daemonic" suggests its origin is divine, mysterious, and independent of his own thoughts.

https://en.wikipedia.org/wiki/Socrates

The Socrates depicted in Plato's dialogues spoke of a daimonion signal that came to him.That word daimonion is an adjective meaning "daimôn-ish" -- divine, or maybe what the English of earlier centuries called "weird."

Anyway the sign came as some kind of voice and Socrates claimed to have heard it since childhood.It was apotreptic rather than protreptic, never commanding Socrates to act some way but only making sure he heard the discouraging word whenever he chanced to embark on a harmful action (Apology 31d).

Xenophon's Socrates heard a somewhat different voice, one that did not hesitate to endorse one action over another.Plato consistently presents an inhibiting divine agent.

Xenophon and Plato agree however that the divine sign of Socrates needs specially to be discussed in connection with the trial at which Socrates defended himself with such famous unsuccess.In Plato's account of the trial, Socrates remarks on having heard no spooky peep that day either on his way to the courts or during his (impromptu, haughty) defense speech.He accepts the news of his death sentence with equanimity and even good cheer on the grounds that since the daimonion did not stop him, the death that will follow his behavior must not be a bad thing (Apology 40a-c).

(Xenophon offers a variation on this last argument but likewise depicts the divine sign practically speeding Socrates along to a happy death.)

http://ndpr.nd.edu/news/24881-socrates-divine-sign-religion-practice-and-value-in-socratic-philosophy/