No, a judge's signature is not required, nor is a court stamp required. The opposing counsel can sign the subpoena. The subpoena does not need to explain why the documents are needed.
It sounds like you have a received a subpoena for production of documents in a case that doesn't directly involve you. You may be a "witness" to the problem the people or businesses are suing each other about. By "witness", I mean you might have information or documents that one of the people/businesses in the lawsuit may be useful to help find more information that is relevant.
Read the subpoena carefully to see if you actually have to "appear" (show up in person) or can just send copies of the documents requested.
If you are not one of the parties to the lawsuit (plaintff/suing or defendant/being sued) you can call the law office in the top left corner of the first page and ask them if you can just give them the documents. They will let you know what they are needing from you.
It is impossible to give comprehensive legal advice in a public forum no matter how well researched. That is why I only give general legal information in response to this type of public question or comment. Before relying on any information given in response to your question or comment, contact a licensed attorney in your state to discuss your particular situation. I am only licensed to practice law in California.