A. B. C.
The A.B.C. Telegraph - the "letter showing telegraph"
1840 Charles Wheatstone and William Fothergill Cooke patented an 'ABC' telegraph in which the rotation of a wheel marked with the letters of the alphabet brought a particular letter to an index mark and transmitted a signal corresponding to that letter. The A.B.C. telegraph had a dial with letters around the edge, one of which was indicated at any point of time (essentially a synchronized stop-clock) - the user noted the letter indicated each time the clock stopped.
Wheatstone, in conjunction with Augustus Stroh, produced a large number of appliances connected with telegraphy and with acoustics.
1858 Wheatstone patented a developed version of the ABC telegraph in which the transmitter sent multiple pulses which stepped the indicator by the required number of letters. This became widely used on private lines or in situations where telegraph traffic was insufficient to justify the employment of a trained operator. Introduced about 1860, this telegraph was used for many years in banks and houses of business as well as in private houses until it was replaced after 1878 by the far more convenient telephone.