IRL Troll Posters are intentionally mocking or ludicrous real-life notices (most often presented in a traditional "missing poster" format). They often gain online popularity through message boards and picture sharing websites such as Flickr, or Reddit, which can result in further copycat examples.
Although it's hard to put an exact date on when satirical posters such as these began appearing in real life, one of the first of such posters to gain an online notoriety was "Look At This Dog" posted to Flickr by Sugar Freak on October 23rd, 2007.
This was soon followed three days later by "Cat Found!!!", which was posted to flick by bezitted (account since deleted) on October 26th 2007. Although it is hard to say if "Look At This Dog" and "Cat Found" are directly related, it is probably no coincidence they appeared online within such quick succession.
"Cat Found" has since gone on to spawn multiple imitators (even popping up on The Best Of Craigslist in November 2008), and has set the tone for many more IRL Troll Posters, all of which follow one of several themes:
Have You Seen This Cat, Because It Is Awesome
First posted to Flickr on June 29th 2008 by Lizzy Stewart.
Propagated by artist Camomile Hixon's "Missing Unicorn" project.
First circulated by British artist David Shrigley
Random Acts Of Design
In November 2010, Minneapolis based graphic designer Phil Jones began a Flickr photo stream called Random Act Of Design which specifically featured the "random designs left up around Minneapolis."