Ref Walt's info about the Benjamin Franklin Fisher (1834-1915) Papers at Carlisle Barracks. There are two boxes of his papers, 1848-1984 (bulk being 1848-1908) at the US Army Mil History Institute at Carlisle. (See the link below, or back-track a search of AHEC via Google.) They do not circulate. Also with them is an inventory/finding aid developed by Col. David S. Kyle, USA (Ret.), who is perhaps (in addition to Dr. Rebecca Raines of the Army's Center of Mil History) best living source on history of the US Army Signal Corps insignia, etc.|
According to on-line info, Fisher's collection includes "key settings" (perhaps for the wartime signal disks) and SigC info of the 1862 period, as well as his prison experience and escape. Col Fisher became chief for a period and resigned from the Army in 1866 as Bvt Brig Gen, to practice law in PA. Perhaps Col. Kyle's inventory might be obtained for our archives, if not already on file or otherwise available on the 'Net.