Keep 'em Wondering
You can buy advertising space just about anywhere these days.
You can buy it online on someone's website. You can pay for one of those big billboards or one of the presentations on the new-fangled electronic type.
Think of all the places you see advertising. There are probably more than you even notice.
Your ad space could be there too.
Just don't post an actual ad there. Leave the space blank.
When the run of your non-ad is over, someone else will fill in the gap.
This may seem rather pointless to you and a waste of time and money. There must be some reason that Buy Ad Space But Don't Post an Ad Day is a thing. If there wasn't, why would it exist?
Think about some of the other special days that people have created. Is there a reason for all of them to exist?
Let me know when you find one.