UML22 — Section: 13.3.25

SignalEvent notation interpretes Signal as an Operation. Details: A SignalEvent is associated to a Signal. The notation of SignalEvent contains an <assignment-specification> that consists of a list of <attr-name>. Quote: "<attr-name> is an implicit assignment of the corresponding parameter of the signal to...". Signal is however a Classifier and has no parameters. Either Signal should be an Operation or the notation of SignalEvent must utilize the explicit assignment of "corresponding attributes of the signal". In the latter case, this assignment should include the attribute name of the signal since the attributes of a Classifier are not ordered.

The issue is correct. What is meant was the attributes of the signal