this question was already raised. Still, I think that one of the weaknesses of CT are formatting tags and it should be dealt with.
I don't think icons (as in leading CAT tools) are needed. On the contrary, I like numbers that represent formatting very much. They are easy to use and don't obscure the text too much.
Would it be possible to add to the numbers a letter following a number, thus, giving basic information what a given tag serves for. In fact, the combination of tags in the current form (numbers) with the letters reflecting additional formatting that already exist in CT (b,i etc.) could provide a great solution. Inserting of tags wouldn't change (a number + ESC) and a letter would be added automatically. Opening and closing diagonal tags (as in the case of additional formatting) would also be of great benefit.
In case of formatting tags in CafeTran projects, there is no need to add more symbols because you can see the actual formatting in the grid and the source segment editor. There are many types of tags (e.g. cell tags, paragraph tags, table tags or simply unknown tags so assigning a symbol to each and every tag is problematic. The best you can do is to save your source document as HTML page (e.g. in Word) and open it for source preview in CafeTran via Resources > Open HTML page for source preview). Then you will have the overview of formatting complexity of your document and maintain the simplicity of format handling in CafeTran.
What if hovering over the tag with the mouse could hint to what it does? Maybe it is too small... just a thought.
Sometimes, the tags' effect show up wrong in the grid (underline instead of bold for instance) although at export it is ok. I can't figure out yet in what circumstances it does that. So at times, a hint could be useful.