It may not be the correct spelling but it's a commonly used spelling it seems
http://www.google.com/search?hl=en&q=marshall
In a country where irregardless and pleaded (what happened to pled?) have become part of the lexicon, i don't think the one or two L's, both of which are used, in marshal/marshall matters that much.
u no wut i meen?
There is no such word as pled, it has always been pleaded. If you are going to offer up an opinion such as this, get it right, or am I asking too much?
Marshal and Marshall are both correct spellings for different words.
Marshall is a proper name, usually a surname, such as General George Marshall, as well as the name of several US cities.
Marshal typically refers to a military or civil authority figure such as US Marshal Wyatt Earp, or, in the case of the military, Field Marshal Erwin Rommel. It can also refer to gathering or organizing a group of people, such a s soldiers i.e. "the general marshaled his forces for an impending attack", military music is called marshal music.
The OKC Marshals makes sense as it is a western town where marshals served as the chief law enforcement entity in the 1800's.