The question presupposes the existence of some standard letters and notations of mathematical objects, which I'm doubtful about in many research areas. My experience with subjects that have a long history suggests that notation in mathematics evolves over time in less than logical ways. In some areas there simply isn't any "standard" notation, while in many others some influential sources have tended to establish a de facto standard. But quite a few mathematicians just make up their own symbols as they go along (I won't name any names), forcing readers to translate according to their own taste. It depends a lot on whose earlier work you most rely on. Even Chevalley, in volumes 2 and 3 of his abandoned series of books on the theory of Lie groups, made some really eccentric choices of fonts and letters.
On the other hand, there are some good lists of LaTeX symbols, as already pointed out. But such a list can only reflect overall usage, not tell you what is currently thought to be "standard" in a given subject area.
