As reported on the BBC news website, a Welsh road sign written in both English and Welsh; the English version read:
"No entry for heavy goods vehicles. Residential site only"
the Welsh, when translated to English, read:
"I am not in the office at the moment. Please send any work to be translated"
That's right, someone emailed the translator and got a reply and assumed that it was the translation - no, it was the out of office message!
Nicely done.