You can define your audience based on tags, alias, and APID.

Setting Tags and an Alias

using UrbanAirship.Push;

// Create a list of tags (tags must be an IList<string>)
List<string> tagList = new List<string>();

// Update the APID with the attributes set in the UI
// Set the new values first here
PushManager.Shared.Alias = "AnAliasString";
PushManager.Shared.Tags = this.Tags;

// Now update them on the server
// This does not need to be called if setting the tags or alias prior
// to calling TakeOff()

The APID is the primary push address for this application and device, but you may also register a set of tags or an alias for this APID.