Presence

I don't care how big an idiot the Rashbam says I am; the Torah's use of karan to describe the light emanating from Moshe's face is an intentional bovine reference. It makes perfect sense! The Golden Calf was in response to the absence of Moshe, not a replacement for God, as the Torah makes clear several times. And while the creation of the Golden Calf certainly led to trouble, the initial instinct to replace Moshe with something must have had some merit, or else Aharon wouldn't have gotten involved.

Now, I'm not saying that the proper translation of karan is horns, because it's not; I'm fully aware of the whole controversy surrounding Aquilas and the Vulgate translation, and the subsequent interpretations of Michealangelo and some farmer in Kasas. But there's any number of other words that could have been used to indicate that light shown from Moshe's face. My point is that the usage of karan is an explicit reference to the bovine in general, the Golden Calf in particular, indicating that Moshe had in some fashion subsumed the role that the Jews had thought the calf would play. Again, just what that role was depends on who you ask; I leave it as an exercise to the reader to fit this in, if possible, to the various commentaries on the nature of the Golden Calf (keep in mind, though, that an eigel doesn't yet have horns, I believe).