New members naturally want to create a signature to list their web site or other information about themselves. Unfortunately, SEO spammers have discovered signatures as well, and have written software robots to search out blogs and add signatures full of links to business websites. Most of the businesses do not know or care how it happens, but their Google ranking jumps.
However, it also turns a blog into a link farm, and runs the risk of being blacklisted by search engines.
Therefore, new members do not get to add a signature until they have posted enough times about actual photography topics that we are sure they are not spammers.
When this happens, their status will be upgraded and they will be able to add signatures. This happens normally after several posts.