Sheets of the London Underground Map writing stamps with the 'Mail Art' label added.
Update Nov 16.
Apparently Tony liked these so much he is going to use them on his outgoing mail. (Google translate does a pretty good job of translating Tony's French blogging into English). He has received so many amazing faux stamps in his mail art project it is well worth browsing through his updates.
And Jean W liked the envelope, so she has reblogged it. So crazy to have this envelope on 3 different blogs.