Watch this space

Hi,
I received a letter from a cyber friend.
At the end of his letter, he said
'Hopefully we can meet again soon.
Watch this space.'
What did he mean by telling me 'Watch this space.'
Thanks.

The space is a noticeboard or hoarding where a new message will be posted shortly. By extension, it indicates that something significant is expected to be revealed soon.

In U.S. terms, it's a message sometimes found on an outdoor sign (billboard) to alert you to an announcement of some significance ... if the billboard company ever gets a new advertiser to take the space. You don't see this very often any more, because it's less expensive for the outdoor company to leave a billboard message standing beyond its lease, than to take it down. That's why the outdoor ad for the Christmas-theme movie is still up in March.