Looking at my Careers profile today, I noticed that I apparently am in the top 10% for the d tag.
I never knew I was that good, especially given the fact that I don't have any activity within this tag. Perhaps I have qualities that are hidden even from me.
However, looking for a more plausible explanation, it seems to me that this should actually be the 3d tag.
In fact, when for a test I add the 3d tag under the "Technologies" section within an "Experience", upon saving it turns into the d tag. When subsequently editing this, it appears indeed that the '3' has been stripped.