Remember, if they are home users, it costs them money to receive your message. If your recipients do not have the same software version you do, they may be unable to read your attachment without using a translation program. Then anyone will be able to read it. Again, respect your recipients' time and bandwidth requirements.
Some stylists recommend a signature with no more than four or five lines.
Consider using a longer signature only for new recipients and an abbreviated signature thereafter. Don't post a virus warning unless you've first checked with an LSCR consultant. Such warnings can be an insidious form of virus in their own right. Unless you're using encryption software, don't assume that your message is secure. Don't send anything you wouldn't want to see in your personnel file.