Gasp! An intriguing prospect indeed. I took a picture for the sake of interest, but I didn't do anything more. But then I saw another one, in the town centre... then another! Then four more! Each one with a piece of jewellery, or a handbag, or whatnot. What could it possibly mean? "Do not return" naturally indicates there was probably nothing to return - well that's my lame excuse for not finding anything.
So what was the purpose of the number (which I've smeared out, but perhaps the experiment would be better served if I didn't)? I called it to find out:
"Hello, and thank you for calling. Please leave your response to this poster"
Huh? My response? Well, my response was to call the number I guess. But the number did nothing to provoke a further action - it didn't give me any criteria to guide my reaction. Was I supposed to say whether I liked it? If I'd found an item? A personal story? I usually like to play along with stuff like this and response in character, but in this case I didn't know what that would be. At least when Danny Wallace scattered his number about London he attached the message "Let's have a conversation". People knew what they were getting, sort of.
I've got a hunch that this stuff was connected to the Art College. Maybe the responses they wanted were just a lot of 'I'm confused' messages. Hopefully other people plucked up the courage to give them!
...but it goes to show that in any conversation, you need not just to be able to hold your end up, but to give the other participant the guidelines to want to do his part to.
What would you have said?