You're talking about the rear sight right?
Ok, I've done a couple of M48s and a Yugo SKS so the two may get blended together here. One of those may not have a removeable pin, try removing the rear sight "blade" first, that may solve the problem. If it comes out, no pin. It's held in by spring pressure, push down on the end where it pivots and pull it towards you.
Hope this helps.