General officers come with flags, placards, and assorted other bric a brac. The rule of thumb I quoted is decades old, and intended to help clarify how all that goofyness should be addressed, and generally benefits joe.
An officer in civvies carrying his uniform with his rank visible is actually an outstanding example of how said rule of thumb precludes stupid shit, because that guy is almost definitely playing the bullshit game… I’d just salute the fucker, ain’t nobody got time fo dat ;)