I think the real point is that instead of the form "-0500 GMT", it should instead be the form "UTC-05:00" or one of the variations I listed in my last post. The fact of the matter is that "-0500 GMT" is simply NOT a usual way to notate a timezone, whether there are parentheses or not.
By the way, the use of timezone names like "EST" and "PST" is really not a good idea because these can have different meanings throughout the world. These are really only meaningful when used internally within a specific country or region.
