The unregistered spam posts were probably a computer program, meaning there wasn't a real person visiting the forum. The recent spam post was likely an actual person who registered. That person was using a dirty method to improve search engine listings for his web site. The idea was to get people to talk about housing prices, then the link in his signature would help his web site for those keywords.
In case anybody is wondering, I am NOT using this message board as a search engine optimizer for my business web page. I'm just cheap and don't want to pay for extra web hosting, so I bought the domain name MtSanJacinto.info and set up masked forwarding (frames). All of the links go back to the main forum file "phpBB2/index.php" which does NOT link to my business web page.
To clarify, it's not a big deal to mention your business or put your business web address in your profile. Sometimes individuals go a little bit further in promoting their businesses on message boards, in the same way that people leave business cards in summit registers. Some other people may be offended by this, and it really depends on how it's done. Please keep in mind that some people visit the wilderness to escape commercialism, and those people may prefer to make friends with others who aren't trying to push a product or service. However, I won't delete these kinds of posts unless they are disruptive, totally off-topic, or if enough people request that it be deleted. If somebody just casually mentions their real estate business in conversation: no worries.