This one bore what I at first thought was a woman's face - a woman crowned, neither young nor old, but silent and perfect in the citrine metal. At last I turned my treasure over, and then indeed I caught my breath; stamped on the reverse was just such a flying ship as I had seen in the arms above the door of my secret mausoleum. It seemed beyond explanation - so much so that at the time I did not even trouble to speculate about it, so sure was I that any speculation would be fruitless. Instead, I thrust the coin back into my pocket and went, in a species of trance, to rejoin my fellow apprentices.
The title of the chapter is "The Autarch's Face," and the head of state would probably be on a valuable coin. So Severian's secret mausoleum is either a former Autarch's, or belongs to an important ruling family that the current Autarch comes from.
Wolfe later uses the coin to cast doubt on Severian's reliability:
This implies that he remembered the coin as having Voldalus' face on it. Wolfe is reminding us that even when we remember something "perfectly," our mind fills in details about things we didn't pay attention to, and can even rewrite memories as time goes on. This is why eyewitness accounts of the same event by different people can vary. This kind of memory revision and interpolation is what makes it possible for us to lie to ourselves.
It was in this instant of confusion that I realized for the first time that I am in some degree insane. It could be argued that it was the most harrowing of my life. I had lied often to Master Gurloes and Master Palaemon, to Master Malrubius while he still lived, to Drotte because he was captain, to Roche because he was older and stronger than I, and to Eata and the other smaller apprentices because I hoped to make them respect me. Now I could no longer be sure my own mind was not lying to me; all my falsehoods were recoiling on me, and I who remembered everything could not be certain those memories were more than my own dreams. I recalled the moonlit face of Vodalus; but then, I had wanted to see it. I recalled his voice as he spoke to me, but I had desired to hear it, and the woman's voice too.
One freezing night, I crept back to the mausoleum and took out the chrisos again. The worn, serene, androgynous face on its obverse was not the face of Vodalus.
It also implies that Severian lies quite a bit. What I find interesting is that he lies to gain respect; in most books or movies, a person lies to "get away with something": to steal something, exploit someone for personal gain, or hide something dreadful. I'm with Wolfe here: I think most lies are told to gain respect from someone. This is hardly covered at all by other works of art. The other main reason I think people lie is to avoid dealing with something. "Lying to yourself" often falls under this category. I guess a lie to yourself can often be a lie to gain respect, self-respect. The avoidance lie is covered better in art, but I think the malicious lie is still way overrepresented. Now that I think about it, media of all kinds like to focus on clear-cut "good vs. evil" scenarios: the "white lie" doesn't make good press, and "stealing your car back from your crazy ex-girlfriend" doesn't make as good a movie as a jewel heist.
Basically Wolfe is saying that no matter how good a person's memory is, you can't believe everything they say. Caveat lector.