100 years ago, dropping the handerchief was considering an indicator of interest (IOI). It was a clear signal of interest.
I have noticed a drop in IOIs over the last 10-15 years. I'm late 30s now, so I've been involved in the mating environment for over 20 years. I noticed that as smartphone penetration increased, IOIs decreased. In the mid to late 2000s, when I was in my early to mid 20s, I got more IOIs than post 2010. IOIs are getting more difficult to come by as women get more immersed in their own worlds with technology. In the few years prior to the pandemic, I was seeing more and more women wearing earbuds in the grocery store, likely to fend off approaches. While I was in college (2001-05), only about 10-15% of women on the general gym floor were wearing headphones/earbuds. By 2011-13, that number was pushing 90% and it has remained there ever since. Walking and hiking paths are littered with women wearing headphones/earbuds. Women are discouraging non-bar approaches in many ways. I realize that a lot of these headphone/earbud wearing women already have boyfriends/husbands and aren't looking for new penis, but earbud penetration is so high that I know there are many single women who are discouraging approaches.
One of my friends did more spam approaching, especially at bars, when he saw zero IOIs. He could get away with it as a 6'4", White ex-college athlete. Most men spam approaching will burn out from lack of outcomes.
I still believe that an approach is more likely to succeed when a woman provides IOIs. I still prefer to approach when I have IOIs vs. when I'm approaching with nothing.