The "Work in progress" and "Showcase" boards aren't made to be used to make "announcements", but actually give developers the change to get feedback on projects that are in development and already have more to offer than just a logo, while the latter is exclusive to finished projects and demos.
If such things as "announcements" were allowed,... oh boy, then we'd have 1000's of threads every month with only a logo and an oneliner - and that doesn't benefit anyone.
The mods would have more work, the people reading through the threads wouldn't get what the heck it's about anyway and all serious projects would recieve next to none feedback.
This forum's mainly used by developers and people that want to become one - so you don't have to try all this fancy advertisement tactics, or announce anything, this is not IGN or whatever gaming site you prefer - just develop your games and post them once you have enough to show.
I'd advise you to read through KeithC's sticky, especially this part of it:
Work in Progress Guidelines
-Doomster
