Yes, your ISP will know that you run a relay. (If you don't want that, consider running a bridge instead.)
Altho the traffic looks the same, the amount/direction is not. When you use TBB, your Tor is only a client. You will have little traffic 'up' (relatively small requests) and more traffic 'down' (the requested content). When you run a relay, the amount of traffic up and down is much closer together. This will indicate that you run a relay.
The list of relays and their IP addresses is public.