As DR alluded to, the use of the wedge was not unique to railroads or necessarily wire-line telegraphy. Radio operators used the wedge as well, although it is most often associated with land-line telegraphy. 

Many 20th Century standard (straight) keys in North America had a "bug lip," which allowed one to slide the wedge into the key in order to use a bug.

Also, it's important to note that land-line telegraphy was not limited to railroads. There is no such thing as "railroad Morse." Morse telegraphy and the American Morse Code was used by....

* Press (wire services such as UP, AP, Canadian Press, etc.)
* Stock brokerages (E.F. Hutton, etc.).
* Commodities exchanges (Chicago Board of Trade, the Cotton Exchanges, New York Stock Exchange, etc.).
* Commercial telegraphy (telegrams, etc., Western Union, Postal Telegraph, CN and CP Telegraphs, etc.)
* Private business wires.
* Telephone Company - land-line telegraph circuits were superimposed ("composited") on long-distance toll circuits, allowing the latter to remain in revenue service while internal telephone company business was conducted in Morse, The circuits could also be leased to private industry.

.....and so forth. While the railroads were important users of Morse telegraphy, and perhaps the last users of Morse telegraphy, it's important to remember that the telegraph was quite universal and it was used extensively in many industries besides the railroads.

73,

JW (WB8SIW)