When athletes sign up for your event, we present them with a couple of neat buttons that allow them to tell the folks in their social networks that they've signed up for your event. They look something like this:
If you've included your event's social media information in your event setup, you'll be tagged in those posts by default.
If you've included hashtags in your Twitter information, those will automatically be appended to the message as well.
Here's how to set that up
When athletes click the Tweet it button after registering, they'll see a pop up similar to this. They'll still be able to edit the text, but your @handle and #hashtags will auto-populate in the box.