It came about when I was playing with letters to make up the club name. MUG gave the right flavour but wasnt specific enough. MUGRO was specific but lost the sense of irony. MUGro was no improvement. Then I happened upon the registered copyright symbol which combines the R and the O in a sort of ready made RISCOS monogram.
Hence MUG® - don't know if the symbol will be rendered properly so I usually write it as MUG((R)