Most mutants, should they have a physical mutation, would never be caught out during the day without some sort of camouflage. Hank had accepted long ago that there was no hiding what he had, especially after his public change. He was an advocate for all mutants and humans alike.
His mind must have been wandering as he settled on the park bench. He had been waiting for the person following him to catch up. Indeed, Hank has acute 'beast-like' senses that allows him to hear distant objects more clearly than a human. He can also track and identify by scent and has cat like night vision.
Hanks head turned as he heard the distant whisper and he waited for an appearance.