Hello, it'd be best to have a complete backup before you upgrade, but in theory 1st Installing 10.6/Snow Leopard, which you need to get Lion, should preserve all those things.
Second best would be to copy tour whole Home folder, next best would be...
On Mail...
First Quit Mail, then I'd backup these two Mail folders, by right clicking on them in the Finder, then choose Archive/Compress.
Users/YourUserName/Library/Mail (Signatures are in this folder)
Users/YourUserName/Library/Mail Downloads
(Could be a different folder here if you chose such in Mail Prefs)
Right click on that Mail folder, choose archive, you'll get everything in the folder, and the folder itself in a file called Mail.zip, move it to a safe place, same for the Mail Downloads folder... only the plist is separate.
/Users/YourUserName/Library/Preferences/com.apple.mail.plist
For Address Book, quit AB...
Files...
/Users/YourUserName/Library/Preferences/com.apple.AddressBook.plist
/Users/YourUserName/Library/Preferences/com.apple.AddressBook.abd.plist
Folders...
/Users/YourUserName/Library/Application Support/AddressBook/