Question: Is it his case number 30-100 or his Case Number 30-100?
Answer: First, thanks for asking the question. According to Gregg, a noun followed by a number or letter that indicates sequence is capitalized. I think since you are describing a specific case with the sequenced number, it is capitalized. If it just said “his case,” then it wouldn’t be capitalized, but it is like saying “his Mercedes Benz” rather than “his car.”
I hope that helps! And if any readers have questions, check out the Ask PTB page on the website proofthatblog.com.