I think we agree that the thunderbolt is used in several countries, although the German one most closely resembles the one on the sword's guard.
Telegraphy corps was certainly the closest ancestor to the radio corps and it too used electricity as a symbol, which is clearly akin to lightning in the imagination of whomever thought of these insignias.
Telegraphy of course evolved from the signal corps and indeed some signal corps insignias show the lighting(s) along with flags.
Also intelligence units have the lightning as a symbol and this comes from the use of " radio" too
http://www.asalives.org/ASAONLINE/herald01.htm
"....The Reserve Army Security Branch was created in 1952 and its badge (Figure 6) contained a lightning bolt, signifying communications; and crossed key standing for secrecy, authority, and guardianship. This Branch was subsequently combined with Army Intelligence in 1962 to form the Army Intelligence and Security Branch mentioned above."
This one is from the US Signal Corp...