If your name's not down

The guest list is very restricted
There's only one name that's depicted
The rest of the people
Use the door by the steeple
That's the rule with which they are afflicted.

The Greek Orthodox cathedral in Crouch End has had a small alteration made to the sign on one entrance. I've never seen anyone here, nor even an open door, but it's such a big building that someone must know something.