US Politics

Of which one is you do not treat people as a means to an end. I.e., no torture, no banning all refugees because it may prevent terrorists from coming.

Kant argued for the existence of an objective moral truth. I don't think this is going to help.

As ever with Kant, you have to be a little more careful than with most other writers when talking about his philosophy in terms of 'subjective' or 'objective'. Most people ignore the first and third Critiques when talking about his ethics, but they shouldn't be ignored. (For the record, I don't think Kant satisfactorily resolved the issues around these concepts even as his thought developed.)

Regardless, I'd suspect that the reference the sign-maker had in mind probably was to aspects of Kant's political philosophy rather than his ethics, although, that said, pretty much any appeal to ethics would have bite against the crew currently acting in violation of them.