Mr Happy wrote:-

"Sorry, there's no keys of U or R"

Well, that is true... but only if you are prepared to be hidebound by conventional musical theory. There is a broader way of regarding keys in music. Let me explain:-

The key of U or to give it the proper title of YOU!!!! -
This is the key much favoured by the duller class of singer/songwriter who pen their interminable ditties about their girlfriends leaving them as in all these songs that begin -

YOU!!!! left me broken-hearted,
I think I'll drown myself....etc.

The key of R or to give it the proper title of ARRRRH -
This is the key much favoured by fake West Country yokel bands inspired by The Wurzels whose songs start with the lines -

ARRRRH The frost was on the turmot-tops
When me and my gal met
Behind the combine harvester....etc.

I hope this clears up your misunderstanding of the broader, more folk music friendly, range of musical notation.