Your email signature can say a lot about your business. Here at Peninsula, we always believe that the email signature provides a lot of information about your business, who you are, what your company stands for and so the right information needs to clearly be stipulated. Also a messy email - inconsistent font, poor grammar etc. - can also portray a poor image of your business.
My advice is to have someone in-house who polices email signatures. This should be a member of your marketing team or your communication officer. All of your employees should abide by the same rules, any variation or different message should be signed off and in-house branding style should be used throughout. Whilst it may seem an unimportant detail, your email signature is a perfect platform in which to market your business and people certainly notice it, I know it is something that I pick up on.