Tri Sigma has never allowed local symbols, we have always only had our national symbol, the Sailboat. This has been the same ever since we were founded. You can find more information on
www.sigmasigmasigma.org or contact an Area Director. If any Sigma's have questions about this, please feel free to contact me privately.
Local symbols are not harmful, please don't get me wrong, and some NPC chapters or local sororities may have them. Tri Sigma just does not. Having one national symbol creates unity, having local symbols differentiates us, which we do not want. Many local Sigma groups have probably kept a local symbol or started one because the national organization or national officers did not know of it and therefor could not educate the chapter regarding this.
Thanks for asking!