plus-ui/public/static/flowable-modeler/editor-app/configuration/properties/signal-property-write-template.html

<div ng-controller="FlowableSignalRefCtrl">
    <select ng-model="property.value" ng-change="signalChanged()" ng-options="signalDefinition.id as (signalDefinition.name + ' (' + signalDefinition.id + ')') for signalDefinition in signalDefinitions">
    </select>
</div>