how to get Exotic loot using "Strange Coins"

Watch out for the Agent of the Nine If you've been schooling extra-terrestrials by way of Destiny's Strike missions this week, you may have stumbled on a mission reward known as a "Strange Coin". I've got a couple rattling around in my inventory, I think. Wondering what they're for? Wonder no longer. As passed on by Gamers Heroes, Strange Coins are obtained by participating in special events such as weekly Heroic Vanguard Strikes, though you'll sometimes be lucky enough to receive one after beating the first Public Event of the day, or by decrypting a Legendary engram. There may be other ways to get ahold of them - by all means fill me in. The coins can be traded for Exotic weapons and upgrades (including perks for Sparrows) by speaking to a mysterious NPC, Xur, who only visits the game's Tower area at weekends. There you go: mystery solved. The only remaining question, I guess, is what's so strange about these coins. I mean, being exchanged for items strikes me as fairly standard behaviour for currency.