A month or so ago Seleene posted to the Mercenary Coalition forums that these coins were going to be created, celebrating Mercenary Coalition's one year anniversary. They are surprisingly affordable, provided you have at least 50 or so people who want one. I got mine in this week and am very pleased with its quality.
It's very hefty, probably weighing as much as my Nexus 5x and is pretty large. I've put it next to a quarter as you can see to the right. The front of the coin has the alliance logo and the back has all the corps who were in the alliance at the time the coin was created (sorry ANZA). It's not elaborate, but I really like the idea of the challenge coin. Seleene got the idea because they did it in Pandemic Legion every now and then. Rooks and Kings also create challenge coins for memorable events. I'm sure we'll continue to make a few more in the future for really cool things, and I hope I can keep adding to my collection. Maybe once I get a few I'll frame them. For now, this one sits on my desk.