(Or, the issue of the disappearing comma of direct address. This section is the contribution of the Queen of Anglophonia, whom this error upsets exceedingly.)
Pooh, you say, who cares about the comma of direct address anymore? Who even cares what it is (or was)? Everyone knows what is meant by a sign reading "Go team!" or "Happy Birthday Mom!" True. But a missing comma of direct address could have dire consequences.
For example, in my heading, the command "Eat kids!" is telling people to devour little children. But if I write "Eat, kids!" I am telling the children to nourish themselves.
Likewise, the statements above should read "Go, team!" and "Happy Birthday, Mom!"
In the future, gentle readers, please ask the cake decorator to take an extra second and add that little dab of icing that will mark you as a literate party-giver. Your more educated guests will be filled with admiration before they fill their stomachs with cake.
Why has the comma of direct address all but disappeared? I have no idea. The rule for its use is a very simple one, far simpler than many others regarding English punctuation. Here it is. Put a comma directly before the name of the person or group you are addressing, no matter how short or long your opening statement. Examples: "Hi, Tom." "How are you doing, Tom?" "Would you like to go out to eat tonight, Tom?" "Go, team!" "Happy Birthday, Lucas and Olivia!" (Lucas and Olivia are twins.)
In an e-mail or other letter to me, please don't start with "Hi Leonore, ..." Instead, write "Hi, Leonore." If you dislike my pronouncements enough, you might write, "You're full of baloney, Leonore." Then go on.
Queen Leonore has spoken. Now move along, folks. There's nothing more to see here, people.
Were I but King of Anglophonia
Eat Kids!