Wandering around, camera in hand, with one’s eyes fixed on the ground and taking photos of weeds and other random objects?
At least, this is more-or-less how we recognized each other the one time so far (to my knowledge) that I encountered another iNatter in person. (It may have helped that the site in question was not the sort of place that one would actively seek out for a nature outing unless one happened to know that it was home to a significant population of a rare bee species – so it was a reasonable conclusion that we were both bee people, if not necessarily iNatters.)
I suppose one could also buy an iNat hat or shirt if one wanted to make sure of being recognized. I don’t live in an area with a particularly high density of iNatters, but I have wondered sometimes whether I have crossed paths with others unknowingly. A couple of times I know (based on observations in the posted on iNat) that I have been out on the same day at the same location as someone else but we seem to have missed each other by an hour or two.