I get a lot of @MarkLaPolla but I have not noticed any special notification. I get notification with or without the use of the '@'. If the '@' is special, how do I use it to send notifications. Thanks.
To complement robjohn's good answer let me just add that not rarely when it is used in fact it does not do anything as user use it in ways so that it will not result in a notification (or indeed will be redundant as you remarked). Very roughly, it can be used only to reply to users already in a communication not to call somebody into a communication. Furthermore the owner of a post is always notified of a comment as well as a unique commenter in a conversation with the own of the posts. Details are at
In chat, the '@' symbol signals type-ahead for names and usually makes an audible ping on the recipient's computer as well as leaving a message in their inbox (the blue inbox icon next to "StackExchange").
In comments, the '@' symbol signals type-ahead for names and leaves a message in the recipient's inbox
As Martin Sleziak comments, your global inbox is accessible here.