As a past holder of a Greek License, through Affinity Groups, greeklicensing.com, I feel compfortable with the following.
Individual letters, Kappa for instance, may not be trademarked. However, if you were to print a bag, with "Kappa", in their color of blue, and maybe include a key you are walking a very thin line. Simillarly, if you were to list them online, with the assumption that they are kkg bags, and reference the name even in the description, you could find yourself in a bit of legal trouble.
There are some organizations that keep track of licensing themselves. However, the concept of Greek Licensing, was developed about 12 years ago, and the largest and possibly only group I know overseeing this is greeklicensing.com.
I am sure that they would be happy to answer any of your questions, but realize that if you call them you will be put on their radar for the future. They will not hesitate to come in and sue any company that is not abiding by the law.
Hope this was helpful!
