some people wrote:SPAM Alarm
If you see a message that is clearly spam, please follow these simple guidelines:
It's faster for me to spot such spam messages if the last poster to that topic is a spammer. This method doesn't work if someone writes a message to that topic, pointing out that the above message is indeed spam. However, if the spam message doesn't get deleted within, say, 12 hours, feel free to PM either myself or the appropriate forum moderator for removal (please include a link to the message).
EDIT: If you're on IRC, feel free to drop me a note if you see a spam message.
EDIT 2, after installing phpBB v3: You can use the "Report this post" functionality when you spot spam messages, it's the exclamation picture in the message.