To continue on matty's post:
Since you already have the Email parameter passed to your OnEvent_Signin function, you can use that to get a Contact object for the contact who just signed in. We'll store that in a variable, such as "theContact". Then, we have a valid Contact object so we can use all of its functions and properties. The one we are interested in is the contact's name, so we make a variable "sName" to store the contact's display name in. From there, you can easily use the "sEmail" and "sName" to display a toast.
code:
function OnEvent_ContactSignin(sEmail){
var theContact = Messenger.MyContacts.GetContact(sEmail);
var sName = theContact.Name;
MsgPlus.DisplayToastContact("Sign In","" + sName + "", "(" + sEmail + ")\nhas signed in.", "", "OnEvent_ToastClicked", sEmail);
}
Since you defined a callback function "OnEvent_ToastClicked" in that call, you might want to make such a function:
code:
function OnEvent_ToastClicked(sEmail) {
//Do something useful here!
}