I created an issue on our local Gitlab instance (10.0.3) to report a ‘bug’ with some of our code and the ® symbol and funnily enough, it rendered it in a giant size 
See image:
This only affects the individual issue page itself, and not /issues where all issues are shown (it renders in ‘normal size’ there).
I haven’t checked if this is the case for ™, © or other such Unicode(?) characters.