Include only the minimum you need from the original message. Quote back only the smallest amount you need to make your context clear. Use some kind of visual indication to distinguish between text quoted from the original message and your new text. This makes the reply much easier to follow. Many mailers can add a signature to your messages automatically.
Signatures are a great idea but are subject to abuse.
Keep your signature short - four to seven lines is a handy rule of thumb for maximum signature length. The length of your quote adds to the length of your signature. Try to avoid topical or local quotes, since they may be meaningless to recipients in other towns, countries or cultures. There are hundreds of others, some more recognizable than others. The Bottom Line Above all else, remember that electronic mail is about communication with other people.