In American English, bills, notes, bonds, and securities issued by the United States Department of the Treasury are Treasurys. The word has an initial capital letter, and it is pluralized in an unorthodox way—with -ys instead of the conventional -ies. We can’t explain why Treasurys is pluralized this way; there are several theories out there, but none is convincing. What matters is that this is how it’s done by people and publications with knowledge and clout in finance and economics.
Of course, when treasury refers to anything but U.S. Department of Treasury bonds, it is pluralized in the more conventional way—treasuries.
And our foreign lenders might abandon Treasurys for a safer security. [Forbes]
The prospect of trouble in the all-important market for Treasurys is only adding to their worries. [Washington Post]
Private foreign investors sold a record amount of U.S. Treasurys in June as the U.S. debt-ceiling debate intensified. [Wall Street Journal]