Snip out everthing not relevant. Signatures, headers, etc. should always be snipped. If a topic only pertains to one person, or is a personal question, consider private email instead. Add something new to the discussion, or use private email instead. Signatures and tags at the end of messages should be short.
Long signatures can take up a lot of space.
Please do not use the list to perpetuate urban legends. A chain letter is any pieve of email that asks or tells you to forward the message on to a certain number of people, regardless of whether it asks for money. Forwarding off-topic messages from other lists or newsgroups is generally discouraged. If you feel the message is particularly relevant to the list and it's of resonable length, you may post it IF you snip all the headers, signature files, etc. Posting any knind of binary file to the list is absolutely prohibited - it causes lots of bounced messages which makes the list administartor very cranky.