The notation Cis(θ) is often sometimes used when writing the polar form of a complex number. For example the complex number r ei θ = r (cos(θ) + i sin(θ)) will be shortened to r Cis(θ).
As far as I can establish, the first use of this notation was by Irving Stringham in his Uniplanar Algebra, 1893. On page 71 I found:
I requested information on the use of this notation around the world on Twitter, and received several responses that indicate it might once have been more widely used.
For instance Matt Jones @doc_jones1 replied that it was used, "Very occasionally in old highschool textbooks in the UK."
This idea of high school usage may be contrasted by the fact that I just found a copy of Abstract Algebra: An Introduction to Groups, Rings and Fields By Clive Reis from 2011 which uses the Cis notation. In searching Google books I found dozens of college level textbooks using the notation.
Luis Biedma wrote from Argentina to say, "We use it here in Argentina sometimes." Ms Kat @hornmaths added that it is used in Australia as well. There were also reports of use in Turkey and Indonesia.
churiah hati safitri @churieheart wrote from Indonesia that "It is used in textbook of calculus 2 at univ. I think it is rather common here."