First what is a pregnancy ticker? It is a graphic often added to an e-mail signature that looks like a 40-42 week time line with a countdown to the birth in X days, X minutes, and sometimes X (!!) seconds. Some "cute" pointer moves along the timeline.
Yikes! A ticker knows to the second when a baby will be born!? A normal gestation is 38-42 weeks when labor is left to start on its own (if you're induced at 38, 39, 40,+, weeks, I consider that premature). What happens when you approach the end of your ticker... and... no contractions? What happens when you get to the end and you don't have a birth?
Two related scenarios come to mind that bring me to my conclusion. The first time I put an inspirational quote in my signature with the intention to inspire others, I found I was the one who the quote imprinted more than anyone else. I saw the quote over and over and over. In the case of an inspirational quote, this is a good thing. I was repeatedly reminded of my purpose. In the case of birth, you do not know when you will go into labor. You do not need to so much focus on your due date. A ticker can only add to disappointment, intervention and anxiety. There are other ways to let people know your pregnant. Typing your due date in your signature is much better then a "countdown" which reminds me of a bomb.
Say other people actually do notice your ticker and the countdown. You're going to have them nagging near the end... its time.... its time... You mean you haven't delivered yet? More anxiety and pressure to preform.
Say you know when you are going to birth because your birth is scheduled, is a ticker still harmful? I say yes, because it it propagates the myth to others who still have a chance to go into labor naturally in the 38-42 week range. Get them thinking that "I must have a ticker, too."
You probably think I am very silly, to care about a silly little trendy graphic, but I see it as a red flag to your own pregnancy. I don't necessarily see it as a sign of a healthy outlook on your birth. I see it as harmful to others. Using a ticker shows me that OBs aren't the only ones responsible for the birth crisis. It shows me that mothers are also focused on getting the baby out around a particular date and don't understand the "normal" length of a human pregnancy and don't understand that labor is best when left to start on its own.
Disappointingly, I've seen natural birth communities promote these graphics.