We voted on a visual identifier for use on pins/clothing/merch a few years ago. You can download a high-quality copy
here.
Another identifier we used for meetups at one point was a black D written on the left hand.
We also voted on a hand gesture, question/answer series, and a code. All of this can be found in the FAQ at posts
>>237. Feel free to petition for a new poll if you think they should be updated.