For those experienced in cold approaching, how often do you spot opportunities where the girl is giving IOIs (before approaching)?

For me, on work days I get about 30 minutes free time in the busiest street of my town, which I spend looking for girls I could cold approach. In the last several months, I can count on one hand the number of girls giving unambiguous IOIs, which feels a little underwhelming. So I'm interested in other people's rates of opportunity.