Blippers meet

Family gathering today in Crickhowell and we were joined by two blippers Cathaber and her partner,OB. ( sorry cant put links from my iPad).

How do blippers recognise each other? Answer with some difficulty in a crowded pub.
I accosted one surprised couple today who seemed to fit Cathaber's description " tall, wearing red with glasses".
I asked if they were blippers and they looked at me as if I had drunk too much mulled wine.
We did eventually locate each other and it was great to share stories.