What does ctrl+r do in Excel, without me bothering to find out myself?

I hit the r instead of the d, and it populated the cell with the word 'No'. I've not copied 'No' at any point today, and I quite like the thought that there is a shortcut for putting 'No' in a sheet rather than having to type it. I have checked if there is a shortcut for 'Yes', but if there is I can't find it.

Anyone?

Bueller?