In fact, most people probably wouldn't notice it was even there but because you know it's there it makes a woman feel very uncomfortable. Well, there are a couple of things one can try. Sometimes they work but one of these ideas isn't too comfortable.
Depending on where the ladder is placed, go to a ladies room and see if you can turn your stockings around. Because the foot isn't set into one fixed position sometimes removing the stockings and putting them on backwards to place the ladder on the inside of your leg or at the back of your leg will help.
Failing that and if you have some clear nail polish, put a dab on either end of the ladder and this will often stop the ladder from running any further. Unless of course, you have actually pulled a hole in your stocking in which case the material may not have actually laddered but has left a hole in your stocking. There's not too much you can do about this except throw them in the bin.
If you have just snagged them and a thread is pulled, don't cut that thread otherwise you will most likely have a ladder and a hole. Snagged or pulled threads aren't nearly as noticeable as you 'feel' they are and if anyone is looking that closely at you it would mean they don't particularly mind if you have laddered stockings or not because they are most likely more determined to get you out of them anyway!