Glyph of Drain Soul
Your Drain Soul ability occasionally creates an additional soul shard.
We might as well call this the Soul Shard specialization glyph -- an extra shard for Drain Soul? Yes please! Even if you pack your bag full with 28 Soul Shards before heading into an instance or raid, Warlocks still find themselves in situations where they run out of it, specially for those who have Shadowburn thrown in. Timing Drain Soul just right so it doesn't gimp your DPS is a pain in itself, so an extra shard for the effort is pure win. Besides, procs like these are like an Azerothian mini-lottery. This is also perfect for those lazy Warlocks -- and there are a ton of those -- who only bring a handful of shards to an instance.