While using GMail today, I wrote somewhere in the text of the e-mail "see attached", but forgot to actually attach a file and clicked the send button.  Guess what, I see a dialogue box with the following message:

Did you mean to attach files?

You wrote "see attached" in your message, but there are no files attached.  Send anyway?

Before posting this message, I played with other phrases like "see the attachment" or "see attachment", and it would prompt me the same message with the quoted phrases (that you write). 

I also observed that this works only when you have a subject line!!