You can assign a Signal only to Send or Call (synchronous or asynchronous) Messages. Only one Signal can be assigned to a Message. If a Signal is assigned to a Call Message, the Message is automatically converted to a Send Message. To assign a Signal to a Message by typing Message name To assign a Signal to a Message from the Message Specification window Names of signal attributes are displayed in the message signature by default. However, you can change this behavior by opening the Symbol Properties dialog (right-click a Message and select Symbol Properties) and setting the Show Attribute/Parameter Names property to true to display them or false to hide them.
To assign a Signal to a Message by dragging