BRASS US MARINE CORP EMBLEM

  It is the Eagle, Globe and Anchor emblem of The United States Marine Corps.  The web pages listed below might help you identify what you have.  Truthfully, it's looks to be a standard Eagle, Globe and Anchor to me.  By it's size,  I would say it might have been on an outdoor placard of a base sign or a door of a HQ building or something of the like. It is hard to tell really.  If you go to any Marine Corps base you will see the Eagle, Globe and Anchor of many different sizes.  Interesting side note, while many Marines call it the "EGA" for short, it is actually considered very improper and disrespectful for the most part.  It should be called either the Eagle, Globe and Anchor -or- the emblem of The United States Marine Corps.  However, I will call it the emblem for simplicities sake.

The web sites:

http://www.usmilitariaforum.com/forums/index.php?showforum=390

http://www.grunt.com/corps/scuttlebutt/marine-corps-stories/lineage-of-the-usmc-eagle-globe-and-anchor/

or search:

www.usmc.mil

(official Marine Corps Website)

All of the above contain  a lot of information about the emblem and it's variant's.  

   Lastly, and not to be disrespectful m'aam (LynneN), but your statement is false.  Although, there were quite a few variations of the emblem before the current one was adopted however, only one authorised version of the emblem had both the lat/long lines.  This version is often refererred to as the "China Marine" emblem or the "Goony Bird". The link below explains it.

http://www.usmilitariaforum.com/forums/index.php?showtopic=57051

   I hope this helps some.  BTW, I am a Marine, so I am kind of in the know ;-)....

Cheers