Invisible marketing can be a great relationship building opportunity. Instead of saying “I get good results, what else is needed?” (a client quote), ask them to introduce you to others in their organization or in their field. If indeed they like your work, they will be marketing for you.
Have you considered testing draft articles or speeches with current and recent clients and prospects? Here again, even if they do not respond, you are showing them your skills.
And where you are involved in pro-bono or charity events, invite your clients and prospects. Another invisible marketing tool for a very good cause.