I've found that whenever an evil rich character laughs in anime they raise their hands to their mouth and let out a 'ohohoho' or similarly annoying laugh.
Where does this mannerism come from? I can now tell someone is rich if they have this style of laugh, but that's because of association rather than understanding
There seems to be a YouTube user called ohohojuo-sama which posts lots of these http://m.youtube.com/watch?v=MM_k1MZB4Ak
The hand raising part comes from old Japanese traditions where refined women were not supposed to show their mouth when they laugh. The fact that a character uses it can indicate that they place a high importance on manners and such which is one of the traits of stereotypical posh characters.
Women covering their mouths as they laugh at the lady falling over after pulling bamboo from ground (Scene of the Twelve Months - Fifth Month (Toyoshiro and Teyokuni) ) 1801
The Ohoho! is intentionally high pitched and annoying - this is to make it sound both artificial and bitchy (which is usually the character's personality)
Kodachi from Ranma 1/2 was the first instance of this trope occurring in anime, however this trait was already in use in film by this stage.