Oxford English Dictionary "coded" under Extended Uses
Sense III.6.
Of words, statements, etc.: expressing a meaning in a way that is indirect, deliberately euphemistic, or concealed from the uninitiated.
1961
This coded language conveys one definite sense and meaning to initiated Communists and sympathetic supporters. It carries an entirely different and deceptive meaning to the non-Communist world.
Shaped by any (unwritten) system of social or cultural conventions or customs; that has been assigned a category, meaning, or symbolism according to such a system. Frequently as the second element in compounds.
1967
In human communication people in social organization perform and interpret repertoires of coded behavior.
American Behavioral Scientist April 8/1
The Oxford English Dictionary weighs in with 1961
and from an anti-communist context
Oxford English Dictionary "coded" under Extended Uses
Sense III.6.
Sense III.7.