Tactically, I believe it is the same, but as a strict translation, it doesn't make sense to me. Unicorn means literally one-horn, so bicorno would mean two-horn. Uni = one; Bi = two.
In the German school, "Ochs" (Ox) and "Einhorn" (Unicorn) are very similar positions (differning only in where the point is pointing, IMO), so perhaps it is effectively the same thing for Italians. The Flos Duellatorium at
www.varmouries.com/wildrose/fiore/fiore.html only gives the English translation without the original Italian with it, and it only lists the guard of the Unicorn in the longsword section. I don't have any idea what posta di bicorno looks like, or even if their translation is accurate, but it makes sense to me that they are similar positions.
But again, tactically, an undercut with the longedge will put you in either the ox or unicorn guard, so maybe I'm just splitting hairs, here.
David Kite