I currently work quite a bit with serial ports in C# and have asked a question pertaining to them. I don't know if the usage would be there to warrant it, but it would be nice to have a serial-port tag for future questions. I don't have the rep, so could someone else create the tag?
For reference, there are 3,542 questions tagged with [serial-port] on Stack Overflow. It's not an obscure or uncommon tag.