In some thread somewhere since PBP 2015 in a YACF forum, I did mention that the next time, I will be having a bell on my bike. Maybe that is what you have seen.
One of my bad experiences in 2015 was not being able to "communicate my intentions" to other riders. For example, very late one night, I got stuck behind two riders, side by side who were meandering about aimlessly all over the road and I could not get past. I was shouting, "Passing on your left", Passing on your right", Passing through the middle, "Coming through" etc, but I still could not get past, if the gap was on the left, soon as I tried to get through it, they would swerve into me, same on the right, same in the middle. They did not even acknowledge that I was there I don't think.
All I can think of is they was foreign and did not understand English, but did I get mad with them. They were swerving all over, like magnets attracting and repelling each other and surprised they did not crash. Eventually though, I managed to get past, so later on, I thought maybe a bell would be handy, the tinkling of a bell is universal to attract someones attention.