Are you a CDT yet?
I have quite a few letters after my name. They won't all fit on my business card, and my email signature looks silly if I include all of them. There are some that I can use just for joining an organization and paying my annual membership fee, which seems too easy. But I proudly display the designations for the certifications I've achieved, because they all represent many years of experience, hours of studying, and rigorous tests. When someone sees my business card or email signature for the first time, they often key in on the designations they're familiar with. Those certifications immediately communicate that I have some level of knowledge about the topic - that I made the investment to achieve the certification. Obviously the letters don't say everything about who I am, but they help with the first impression and then it's up to me.