I thought this was a "no smoking" bike, then I decided it was "pro smoking" but now I've been told that it is, in fact, a "no smelly socks" bike.
Apparently, circles with red borders indicate "no" in the Netherlands.
Lines across signs do not mean "no" like they do in the U.S.
They use the line across a sign as an indicator of leaving a town.
All towns have signs both for entering and exiting.
Here's a "leaving Leiden" sign. It's not a "no Leiden" sign, that would have a red border.
Now, whether or not those are bent cigarettes or smelly socks is still debatable. It is parked outside a student dorm so smelly socks is a very likely candidate.