Yep. A nod will suffice for greetings in almost all public spaces. When I recognize the tell-tale signs I've been 'marked', I am always prepared to respond with

Yep. A nod will suffice for greetings in almost all public spaces. When I recognize the tell-tale signs I've been 'marked', I am always prepared to respond with the unusually effective "negative" response and leave it at that.