does this makes sense?

subscriber.cs

using System;
using System.Threading.Tasks;
using Microsoft.AspNet.SignalR.Client;
using Microsoft.AspNet.SignalR.Client.Hubs;
using TecUnica.Core;

namespace TecUnica.PubSub
{
    public class Subscriber : ISubscriber
    {
        private readonly HubConnection _connection;
        private readonly IHubProxy _hub;

        public Subscriber()
        {
            _connection = new HubConnection(ConfigurationHelper.GetConfiguration("TecUnica.PubSub.HubUrl", true));
            _hub = _connection.CreateHubProxy("PubSubHub");
        }

        /// <summary>
        /// Subscribe to a topic
        /// </summary>
        /// <typeparam name="T">type of object the action will receive</typeparam>
        /// <param name="topic">topic</param>
        /// <param name="handler">action to be executed</param>
        public async void Subscribe<T>(string topic, Action<T> handler)
        {
            _hub.On(topic, handler);
            await _connection.Start();

        }

        /// <summary>
        /// When the connection stops
        /// </summary>
        /// <param name="handler">action to be executed</param>
        public void OnDisconnect(Action handler)
        {
            _connection.StateChanged += state => { if (state.NewState.Equals(ConnectionState.Disconnected)) handler.Invoke(); };
        }

        /// <summary>
        /// Unsubscribe from topic
        /// </summary>
        /// <param name="topic">topic</param>
        public void Unsubscribe(string topic)
        {
            if (!_connection.State.Equals(ConnectionState.Connected)) return;
            _hub.On(topic, () => { });
        }
    }
}

_hub.On returns an IObservable... so you can store a ref to it and just call dispose when you want to unsubscribe

_hub.On actually returns IDisposable

LOOL i wrote iObservable.. thanks David