Your code looks to be correct.
Where in your Urban Airship project are you checking for tags?
Tags are used for sending push to segments of your audience.
The first way I would check if the tags are added is by using the Tags getter method:
List<string> tags = Airship.Instance.Tags;
Next, when sending a push in the dashboard, use the Target Specific Devices option to create a segment composed of one or more tags. These tags would be the ones you set in the app.