Respond with your expertise on the topic and end with your signature. Using your signature to explain who you are and what you offer is the discussion list equivalent of the business card. Just as you don't force your business card on everyone you meet, you don't force your information on the discussion list members. Rather, you participate in discussion and use your signature at the end of every message you send. That's because every list has its own personality.
Some lists are light-hearted and funny, even when the topic is fairly serious.
Other lists are rigidly serious and pedantic, while many tread a middle ground. To find discussion lists in any topic, search on the topic in a search engine or start at the discussion list directory Web site. Join the lists that sound interesting and read the messages for a few days. Evaluate the expertise of the people sending messages to the list, and evaluate the tenor of the list. You will quickly see whether the list will be useful for you.