"Because we have fewer legions than characters, we're able to be more hands-on with legion name collisions. Our customer service team is going through active and inactive legion names, and we will be changing names based on specific criteria (legion size, contribution points, and so on). Similar to how we are handling name changes, if your legion's name is changed, we will be adding a two-letter designation derived from the name of your original server to the end of the legion name and giving your brigade general a legion name change coupon. You'll notice changes to legion names over the next couple of days leading up to the merge," Hager explains.
You can read the full feature on the official Aion website.