First the TL;DR: Adding this tag will help people understand screw theory better and make Q&A on the topic more clear.
Now the long version. I've been an on and off user of the Robotics SE for a while now, and I've come to realize that there are enough questions and associated confusing answers popping up about screw theory that it should probably have its own tag to help those of us who are looking to answer these questions to find and follow them, and those asking to get better answers.
There are now several textbooks and many papers/chapters that use screw theory as their foundation (the most well known probably being the "Modern Robotics" textbook by Lynch and Park and the books/articles/chapters by Roy Featherstone), so there are already many associated questions from students, roboticists, and academics who are using these materials.
Unfortunately, most of these posts are showing up tagged with kinematics and/or dynamics, when the heart of the questions are generally asking something about the screw theory part of the problem and not the core mechanics. Answers to these questions are then regularly constructed using more traditional rigid body formulations instead of screw theory methods, which both confuse the issue further and can potentially cause the questioner to doubt the use of screw theory for their application.
To mitigate these issues, I would like to propose the addition of a "screw-theory" tag on the Robotics SE. I would be happy to go through and tag all the questions/answers that use screw theory already (generally, any that reference "Modern Robotics", Featherstone, spatial vector notation, 6D vectors, Lie groups/algebra, etc.) once the tag has been created.
I believe this will help both the questioners to clearly define what kind of formulation they are using and/or hoping to learn more about, as well as helping those of us who want to answer these types of questions to find them.