In answer to MSKKG's question about recruitment/greek week shirts, at my school we just spelled out the names of all the GLOs. We have two sororities (AEPhi and Theta) that don't allow anyone but initiated sisters to wear letters, so the Panhel rush shirts have the names of all five orgs spelled out.
As for when you become a brother or sister of your org, IMO you're not a full brother or sister until initiation. There are certain privileges reserved for full members, depending on the org. For AEPhi one of those privileges is wearing letters, for other orgs it's wearing/displaying the crest, for most orgs the right to wear the badge or pin an S.O. with it is reserved for full members, etc.
But while you're a new member, you should be treated as a sister in certain regards. We are proud of our new members and encourage them to represent AEPhi by wearing their new member ribbons or pins and/or the letters spelled out - heck, the first thing we give them is a bid day shirt. If I saw an AEPhi NM drunk at a party, I wouldn't say "oh, she's just a NM, she's not my sister" and walk away - I would take her home and take care of her just as I would for an initiated sister. (OK bad example
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During the NM period, NMs are learning about their new org and getting to know the sisters and each other, and figuring out whether they really want to go through with initiation. Meantime, the org is evaluating the NMs. In most NPC orgs, the bid means "we want you as a sister" and it's tough to force someone to depledge, but if one of your new members turns out to be an ax murderer, I doubt nationals would balk if you asked her to depledge
But you're still not a full sister until you have completed your new member education and you are initiated.