My company has a ton of marks that they use in their company communications: copyrights, registration symbols, trademarks, etc. No matter what I did, they displayed so small as to be unreadable. Apparently, marks rendered in Calibri, the standard font for much of SharePoint, render too small, but if you change the font to something like tahoma, they show up fine. Since there is no way in css (or none that I know of) to target an html symbol, I wrap all marks in the sup tag, which raises them a little, like a mark should be anyway, and I changed the font-family attribute of the sup tag instead. Works!