Because they're not your
preferred methods of marketing, this doesn't mean they wouldn't (or couldn't) be useful for others
... or that they're not the preferred methods for receiving information on the part of some customers.
(Which really should be the important point, shouldn't it? Good marketing is not about what we
want, but what our customers
want. N'est ce pas?)
If we're wondering why people don't use the signature option, I think it's a fair -- and related -- question to wonder why they don't make use of the social links option in the sidebar. After all, they're both related to marketing one's business, and they're both set up through the member profile.
So personally I think it's a fair and reasonable extension of the original topic to include this additional information for those marketers who choose to fish in different channels than you do.
Besides, that's one of the exciting differences between a forum (or other social site) versus, say, writing articles. Once the original statement or query has been posted on a community-driven site such as this, one has limited control over the direction the discussion goes from there. The community takes over and the conversation goes where it will.
I learned a long time ago I get a lot less heartburn if I just go with the flow and not get too bent out of shape when the discussion goes off on tangents.
And to go back to another point, I think you may be underestimating the number of people who deliberately choose to not use the signature option. In my years as a moderator here and on other forums, I've seen many
posts from business owners who don't want to tip off their customers or their competitors
they're asking for advice -- especially if they have some specific business problem they're trying to solve. They don't want their customers to think they don't know how to run their own business, and they don't want their competitors to gain any competitive advantage by learning more about their internal issues.
And for this forum in particular, we get a lot of posts from people who are looking for a business to start -- in other words, they may not put a signature link to their business because the business doesn't exist yet.
That said, I'm sure ignorance of the option is indeed a major factor, and it's never a bad idea to remind people of the available resources. All
the available resources.