Small usability issue, but it might be pretty simple to fix. On the signups tab of the user profile page, if the user isn't signed up for any nodes they see this message: "This user has not signed up for any matching content." Could that be a little more user friendly?

Maybe do a check whether the user is viewing their own profile or someone else's, and for whether they've filtered for open, closed or any signups, then print a more tailored message such as "[You have][Username has] no [null][open][closed] signups. Click above to see what's available."

Or let the administrator customize the message with replacement tokens, and if they want the above they'll have to make a custom token to check for profile ownership.