One gamma and two sigmas (they're from the Greek alphabet).
http://ancienthistory.about.com/od/greekalphabet/Greek_Greek_Alphabet.htm
Tau Gamma Sigma was created on 1969-01-17.
Sigma Gamma Epsilon was created in 1915.
Sigma Gamma Chi was created in 1967.
Yes...Gamma Sigma Sigma is not an NPHC organization, therefore, you may be a member of it and an NPHC organization.
Gamma Sigma Zeta was created on 2000-02-02.
Lambda Sigma Gamma's motto is 'Unity Through Sisterhood'.
Lambda Sigma Gamma was created on 1986-10-24.
Gamma Iota Sigma was created on 1966-04-16.
The motto of Sigma Lambda Gamma is 'Culture is Pride, Pride is Success'.
Beta Epsilon Gamma Gamma Alpha Rho Sigma was created on 1923-12-20.
Gamma Sigma Sigma
Gamma Omicron Delta Sigma was created on 1990-07-07.