As our dear Seamus found:
Note that Ronnie often substituted "costume" and "wardrobe" for "uniform", throwing back to his actor days....he is commander in chief and civilian clothes are his uniform...
But yeah, Madge has it right, no acknowledgement at all is actually required of POTUS, and often none is given when entering (for example) a formally-guarded building and the guards 'present, arms!' silently as he enters the facility. They (the guards) wait for him to pass, then resume 'order, arms!'. It would be the same at Marine 1 or Air Force 1, except Ronnie wanted to get personal, and started the new tradition.
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