It's merely coincidence seeing it on Runescape. However, if you don't know what 666 means it's the number of the devil.
Personally, I don't care. It doesn't bother me, and I won't let it. 666 is a number just like any other. Next we'll be hating on colors for some really stupid reason. Oh, wait...
I pack your things and run! but give me your RS account?
Naah I joke the only I really think of 'The devil' is from south park, he seems nice enough on there ;P