What is the most effective way to send social signals via Twitter and to be noticed by someone whose tweets you share?

Retweeting their post and including their @username directly notifies the user that you've shared their content, sending a strong social signal and increasing the likelihood of them noticing your interaction. Liking a post is a weaker signal and doesn't guarantee a notification. Following them and mentioning their real name in a tweet won't notify them unless their real name is also their @username, which is uncommon. Adding them to a Twitter List is a private action and doesn't send a direct notification or social signal to the user.