The exact rules for when and how to engage a familiar face were ambiguous even before half of everyone’s faces were covered by face masks. Flashing a quick smile and quietly breathing a “hey” was a safe bet, but that dialect of body language is dying quickly. “Smeyesing” only goes so far, and squinting can mean anything from a pleasant grin to a death glare.
Instead, here are some alternative ways to politely acknowledge the presence of someone familiar, in some not-so-familiar ways.

Foot Tap

Tapping toes together seems like a culty, secretive exchange — which is an accurate assessment — but it also makes for a hands-free, hardly-touch greeting, like using those tap-to-pay card readers at fancy juice places.

Elbow Bump

The elbow bump is the most close quarters greeting enumerated here, though it also allows participants to hold/interact with something with both hands. Also called “the service industry see ya” by no one (yet), the bump is ideal for passing acknowledgement of an acquaintance. Elbows are socially suppressed on a grand scale by sneezes and deserve a renaissance of everyday application.
Sensei Bow
While most fitting when entering a dojo, a shallow bow from the waist can act as a courteous and respectful gesture to another. This is a fairly hands-free process and is best performed by keeping one’s arms pinned to their sides. I suppose a namaste position works just as well.

Finger Guns

Finger guns while pointing at someone are best accompanied by excited expressions like, “There he/she is!” or “Just who I was hoping to see!” This verbal excitement gives the gesture an upbeat context and confirms that you are not actually threatening that individual with violent acts. This can be by far the most captivating or most dangerous approach on this list, so make your intentions clear with a smile. Or, for the more daring finger gunners, give your firearms a crackle by snapping at your victim — or, rather, recipient — while bidding your greeting.

Jazz Hands

Flashing some jazz hands is a great noncommittal hello that avoids the social and health risks associated with touching other people at the moment. Unless one’s hands are occupied with something other than jazzing, it takes little-to-no effort to exchange a round of jazz hands. If you’re too embarrassed to single-handedly bring traditional jazz hands back to the forefront of common communication, giving only a shake or two of the palms is a more subtle approach.
Some basic conventions may be forever lost in the wake of COVID-19. Wearing a mask has stripped away my dimples and the advantage they give me in conversation with grandmothers. People with intricate mustaches suffer in silence. Demand for nose and lip tattoos has plummeted. Practice your bows and bumps because the world is changing in a not very big way.