Somebody recently smuggled this sticker onto the empty white space beside a bossy parking notice on my street.
It made me smile. And I daresay it made other people smile - though perhaps not the person who seems to have tried to pull it off, before having second thoughts.
It seems that the originator of this sticker (well, OK, it was me) has been reading books on Happiness, such as those by the Buddhist monk Matthieu Ricard, the economist and peer Richard Layard, and others.
Psychologists have studied the effect on a community of just such signs being put up here and there, and discovered a marked increase in happiness. This shouldn't really be surprising - it's a quite obvious, upbeat reversal of the dismal effect on commuters of notices warning us to look out for potential terrorists in our midst.
All too often it seems that being concerned about the environment means getting your knickers in a twist about something ghastly happening a very long way away - South American rainforests, south Asian rivers, Arctic ice shelves - about which we can do very little.
Might we be better off tackling the environment in our own neighbourhood? It's possible. Indeed, if everybody did that, the whole world's problems could be resolved at a stroke, without any interference from governments and multinational businesses - or indeed multinational green pressure groups.
I should point out that the sticker is home made, using harmless inks on the back of a used piece of recycled paper waste, and stuck to the sign using wheat paste. I got the idea for that, as for many other things, from The Guerilla Art Book, by Keri Smith.