The tab may be for some kind of cord. Most snowboard gloves have cords so that they will not drop if you have to take them off, for example on a lift. Further, soft snow can cover almost anything. It is better not to lose stuff. We also used such cords in the Army, where we referred to them as idiot cords. The one on your pistol is called a lanyard, but the effect is still the same. No one wants to risk losing gloves, compasses, weapons, etc. I can see some good reasons to remove a cycling glove briefly while riding. It would be nice if you did not risk losing it.