what to do? Nothing at all. Ignore.
Pretty much this... What would you want the SP to do if you were out on a date, with friends, with co-workers, or with your family? Nothing at all. When I've seen dancers in public, the most I've ever done is give a very discreet appreciative nod and smile. That nod has never been any more than what I'd give to any woman I got caught looking at. (Err, I try not to ogle as a general rule, but, I'm a guy.)
A number of years back there must have been an apartment that had a couple of dancers, and their dancer friends, in it right near where I was staying. I kept bumping into them in all my local (to there) haunts. It was all well and good, with nothing more than minimal acknowledgement when we'd pretty much trip over each other. Then on a date I ended up with a table of dancers (and mostly women friends) a couple of tables down. Other than a couple of quick glances, and probably more squirming and sweat on my part than was strictly necessary, everybody was 'cool'. Thank you dancers.
So, yeah, extend any sexworker you see in public the courtesy not trying to make anymore contact with them than you would any other woman in public. How do you know her kid's not right around the corner? Or a SO? Or friends and family who don't know how she makes (some of) her money? Then hope any sexworker you've met extends you the same courtesy. THE ONE AND ONLY EXCEPTION IS IF THE CLIENT IS VISIBLY ALONE AND THE PROVIDER APPROACHES THE CLIENT.