In sequence diagrams, you can show operation signatures or message
signatures of individual messages to visually represent communication in interactions.
You must have a sequence diagram open that contains messages.
To show an operation or message signature, in the diagram editor,
right-click a message; then click .
The operation signature or message signature is displayed in the name
compartment.
Note: If the message has no arguments, the operation
signature of the message is displayed. If the global preference Show
Operation signatures instead of Message signatures is selected,
the operation signature of the message is always displayed.