Yes, as others have said, "guessing is okay". It's part of the fun of joining in a chat thread. We had great fun on the Unforgotten thread studying all the flash backs from the episodes and trying to piece the story together as it went along.
I am liking the idea of the code being based on the telephone number or coordinates.
You have really got me thinking again and I might have to re-watch a couple of parts.
----------------
Right, we don't know what the phone number is but in episode one, Danny is talking to Scottie:
"So we're on the doorstep, saying goodbye and I'm trying to give him Pavel's nymber, because I don't have a phone... except he doesn't write it down! And I'm like... "If you don't want to... If you don't want see me again..." And then he says, "numbers Danny, I have no problem with," like he could remember every phone number in the world... and then... we shook hands!"
---------------
Episode two - the chat with the American (with the sweet)
American: I have a sweet tooth. It's easier to quit smoking, I swear. Not very British, talking to strangers, is it? I've worked in your country for ten years now. Do you own a house?
Danny: No.
American: A car?
Danny: No, nothing.
American: Well, you have your health. That's the most precious asset of all.
Danny: My health?
American: Lots of people think they have nothing to lose, but in my professional experience, they just haven't thought it through.
Danny: Are you threatening me?
American: Threatening? My, oh, my! This is just a conversation, a chitchat. Two people passing in the night. I can see why you're so confused, over the years I've adopted quite a few of your country's customs, but that great British reserve escapes me. I enjoy talking too much. And, once in a while, someone unexpected tells you something... that might save your life. Be sure to put that card someplace safe.
[But we know that Danny tears up the card and has to re-draw it in episode three to ask Rich what it means.]
----------------
I still haven't figured out any coordinates (episode one) or read the writing on the medication when Sara found it (episode three). I'll be back later.