Where on the holster is it?
Some Black Hawk holsters have a retention device above the trigger, you push the hook-like button to release the catch which holds the trigger guard so the gun doesn't come out of the holster. These tack some extra discipline to use, though, since the pushing in of this while withdrawing the gun can lead one to put their finger on the trigger well before they are on target. On must learn not to bend their joints when pushing it in, so that their finger comes to rest on the outside of the trigger-guard when it clears the holster.