FAR 23.811. The Notice of Proposed Rulemaking. Notice No. 63-42; was issued on 23 Oct 1963.
The change that introduced the requirement was Amd 25-1 and it became effective 7 June 1965.
FAR Part 25 Sec. 25.811 effective as of 06/07/1965
"25.811 (h) Each emergency exit that is required to be openable from the outside, and its means of opening, must be marked on the outside of the airplane. In addition, the following apply:
(1) There must be a two-inch colored band outlining the exit."