I got this from the Delta Gamma National Website:

No Alcohol Statement and Policy:
Statement on Alcohol Use -
The objects of the Delta Gamma Fraternity shall be to foster high ideals of friendship among college women, to promote their educational and cultural interests, to create in them a true sense of social responsibility, and to develop in them the best qualities of character. (Delta Gamma Fraternity Constitution, Article II)

Delta Gamma policy states that no alcoholic beverages may be served or stored on Delta Gamma property. The Council of Delta Gamma recommends that alcohol awareness and educational programs be an ongoing and integral part of each collegiate chapter's programming throughout the year. Council encourages members to identify with the concepts of responsible drinking and individual choice.

No Alcohol Policy:
No alcoholic beverages may be served or stored on Delta Gamma property.
Note: Property is defined as houses, apartments, lodges, suites, dorms, dorm floors and meeting rooms. This includes yards, driveways, sidewalks, and parking lots owned, rented,leased or designated for Delta Gamma use by house corporations or chapters.
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The NPC has a short blurb on alcohol here: http://www.npcwomen.org/images/NPCproject_5.gif

I think if you go to any National NPC sorority's website, they will have a statement regarding their alcohol policy.

As for your college chapter and "can you wear letters if you are smoking or drinking?"...think of it this way: Would you smoke in public or get wasted if you had a name-tag on that had your First Name and Last Name on it? You probably wouldn't, as you couldn't hide behind anonymity, and if you were behaving in a manner which was "unbecoming", you would be noticed (as would your name). Similarly, it is my opinion that GLO members shouldn't wear their letters, if they're going to smoke or drink. Greeks have to do enough damage control as it is when it comes to how we're perceived by the public community at large, and this is how the "one bad apple spoils the whole batch" comes into play". If one GLO member is wearing letters which identify the group to which they belong, and they are behaving in a manner which is unbecoming, people may see this and brand the whole group as "Oh, I guess all XYZ members behave that way." Then the entire group has to work doubly hard to improve their public image. As the saying goes, "it takes YEARS to build up a good reputation, and SECONDS to destroy it". I know it isn't fair, and it kind of sucks, but such is life.