The use of monograms/initials may have been common among intelligence operativs at that time. Shackley's close companion Thomas Clines, who was convicted on income tax charges related to Iran-contra, used (at least) two secret Swiss accounts, one in the name T.C. and the other in the name C. Tea.
Found in Chapter 11 of the Walsh report, the special prosecutor's report on Iran-contra.
Didn't Clines get prison time on those charges?