Scripting Apple Mail

Thank you Chris!

Thanks for AppleScript books recommendations
I used this workaround for Mail signatures:

tell application "System Events"
	tell application "Mail" to activate
	tell process "Mail"
		delay 0.9
		click pop up button 2 of window 1
		delay 0.01
		keystroke "R"
		delay 0.01
		keystroke return
		delay 0.01
	end tell
end tell