At our local hackerspace, we use big flashing lights and an automated system that alerts everyone in the space that its cleanup time, that everyone should clean

At our local hackerspace, we use big flashing lights and an automated system that alerts everyone in the space that its cleanup time, that everyone should clean up no matter what, and that it is unacceptable for anyone to not be cleaning up for 15 minutes. This results in a huge flurry of activity and a lot of walking around looking for things to cleanup and in fact it works. The space stays relatively clean.