"TIAS" refers to Treaties and Other International Acts Series, an official compilation of U.S. treaties. Older citations to TIAS look like: T.I.A.S. No. 10,814. Citations from 2002 forward use a year and number designation: T.I.A.S. 02-1003.
TIAS can be found on the State Department's website, in HeinOnline, and in print.
For more information about treaty research see A Guide to Treaty Research or the Treaties and International Agreements guide.