You know you're not on the UnderGround any more when:

• standing on the left on a travellator just seems wrong
• if a space opens up on said travellator, you can't help yourself from running on the left, even though you have nowhere to be but lazing in a park with a lemon gelato
• you're totally disoriented by the lack of a logical, stylised representation of the totally illogical train lines, and end up getting off the A line, walking around the platforms like an idiot, until someone tells you you need to be on the A line going in the same direction you originally were travelling in
• there's no gap to mind
• the "next train" timer goes from 4 minutes to 1 in the space of 30 seconds, not the other way around
• you don't need your ticket to get out of the metro. Or, sometimes, in.
• it's less economical to buy a weekly ticket than to buy individual trips. Because instead of £4, a one way trip costs €1. Genius, really.

Librarian Traveller Out.