You can write a special announcement on the forum with a free and minimal plugin, and easily integrate this announcement into your theme to get a stylish look.
Hide/show desired user group.
Add custom announcement to each forum
Show your announcement in any area you want with 4 different locations.
1. In-topic editor above.
2. Off topic for topic
3. Topic list above
4. Topic list below
You can use all locations at the same time...
