[jstarfish]

Common courtesy would have one remove the posters once either the animal is recovered or hope is abandoned. That's a pain in the ass though and you likely won't remember everywhere you posted bills while distraught.

The next best thing is putting a timestamp or expiration date on it so you don't waste the time of the samaritans willing to dragnet for you.

I do get where you're coming from though. Dates don't really matter to me since I habitually check corners and undercarriages at night looking for lost anything (I know where all the rabbit warrens are and have found two dogs, many cats and an unconscious human), but if I know there's a current/recent APB, I'll focus my attention while I'm out and about.

[fsckboy]

it's a piece of paper tacked up outside... rely on the wind/weather/humidity/sun to curl/yellow the page and take it down when it looks old.