How banner planes pick up their banners
 

I always wondered how they did this?

Source Herald Sun - How advertising planes pick up their banners

I saw this happen for real right in front of me.

In 1969 I had to take a Cessna 172 out to Hoxton Park and back from Bankstown. On the return leg, I was holding for an arriving aircraft, and only realised what they were up to when the banner shot into the sky - amazing sight from close up, the banner accelerated so quickly.