I had not realized that we had this topic. I believe I explained my username in my introduction thread, but it's probably buried by now so I suppose I will explain it again.
I originally came up with my username when I had to sign up for AO3. I had a couple of usernames that I had been using on various sites since I was about 14, but I didn't want to use either of those (1. because they are from fandoms that aren't important to me anymore 2. I don't like them as much anymore, and 3. I didn't want my new accounts to be easily traced to the same person/same "me" who created the old ones) since I wanted something different. I knew on AO3 I would be reading and posting a fair bit of Sherlock stuff, so I wanted to relate it to that, and I didn't want to have to create a username with numbers in it (my old usernames on other sites have numbers, but I'm not as into that anymore). My other important thing that I like is a musical and film called Hedwig and the Angry Inch, which is about a rocker telling essentially her life story in flashback (mostly). There are awesome songs in it and I think it's a great text. One of the characters in that is named Yitzhak. I especially grew to like the character of Yitzhak through Lena Hall's portrayal of him on Broadway. In a flash of (supposed) brilliance, I realized that if I took "Yitz" from Yitzhak and "ock" from Sherlock, it made "Yitzock" which is pronounced almost the same as Yitzhak (at least in my accent). Hooray for wordplay! I liked how it combined two of my most favourite things, so that's what I chose. And then when I signed up for this forum, I went with the same thing.
My avatar, in a shocking turn of events, is also what I use on AO3. I found the picture of Sherlock and John at some point and saved it since I like Sherlock in the deerstalker. I edited the colours a little bit and resized it and have thus been using it as an avatar here and on AO3 ever since.
My signature was originally just the green letters that say "Clueing for looks" (as some of you may remember from almost a year ago) but then I decided I wanted a small picture, too. I used to make bar signatures like that when I was on another forum years ago (I don't think it exists anymore, since when I went to find it recently I would just get a "page not found") so I thought I would do something like that for here, so I made one for Sherlock and one for John.