Menasha, Wis., and Albany, N. Y. Mathematical Association of America. Inc. February 1950. First Edition. 73-146,  pages. 10 x 7 1/8 inches. Publisher's original printed blue wrappers. Heavily soiled front cover and first leaf. The paper by Shannon is found on pages 90-93. Upper corner bumped. A decent reading copy. Fair. Wraps. 
The American Mathematical Monthly first published this article in Vol 57, (Feb. 1950), pp 90-93 [as here]. We offer here an example of the entire issue in the original wrappers. Other articles include one by Nowlan on the Objectives in the Teaching of College Mathematics and several others.
"Symmetrical notation offers attractive possibilities for general-purpose computing machines of the electronic or relay types. In these machines, it is possible to perform the calculations in any desired scale and only translate to the scale ten at input and output. The use of asymmetrical notation simplifies many of the circuits required to take care of signs in addition and subtraction, and to properly round off numbers." (p.93)
"At the close of the decade, the [American Mathematical] Monthly published a beautiful, long paper by Andre Weil called the Future of Mathematics. It also published a short note in computer science by Claude Shannon called "A Symmetrical Notation for Numbers." Both papers foretold the future of mathematics." (Ewing, p. 134)
(Kuenzig Books stock, NOT shannon files)
Sloane and Wyner, "Claude Elwood Shannon Collected Papers," #57
Ewing, John H., "A Century of Mathematics : Through the Eyes of the Monthly", p.134, 201-204.