Approach switched me to Tower and they said I was number 3 for 18 right and cleared to land." I could not see the two in front of me because of the ground clutter. I replied "cleared to land number 3 18 Right." Then I said "I have them on the IN but not the eyes." Tower said "roger you have plenty of spacing." How do others let the controllers know that you can't see the traffic but know where they are due to technology?