I'm thinking of raising rent on my tenants before leaving the country without them knowing
What is your reason for wanting to raise the rent?
I think it's a nice way to mess with my tenants without even harming them.
Wanting tenants to pay a higher rent is normal but you should follow steps to make sure that you are being fair. It might even be illegal to raise the rent without letting know. It is also not fair to them and they could just move out leaving you with no tenants.
I'll be posting a notice online, so they will read it. They'll also know where to mail the checks even if they don't notice the rent increase.
Well it is good that you are posting it online. May also be a good idea to send them a letter or slip one under their door as well. This leaves no doubt that they know of the rent increase, as doing it without telling them is pretty immoral.