A registered trademark symbol "circle r" is usually meant to add information to a marque or a word. It is superscripted just like the standard trademark "TM" symbol as its a sort of note, in much the same was as an asterisk is used

The Copyright glyph, however, is used as an abbreviation of the word to be used inline as a word in its own right (usually as part of a copyright notice), rather than as an adjunct to another.

However, just as T&Cs are coming ever smaller, commercial pressures, usually from the legal department of a corporation, have resulted in the circle r becoming increasingly big, to the point where it takes on the characteristics of a fully blown character, sitting on the baseline.

From a practical application sense, and aesthetic reasons, the copyright and registration marks were designed in the two sizes for text and display applications.

The old hot type specimen books I have all show both characters the same size. These characters were never part of a normal typeface, but part of a set of universal characters that could be used with any typeface. If a digital font follows the traditional model, the two characters would be the same size, and this is generally the case with most digital typefaces.

But I think many recent type designers (me included) have changed the proportion of these characters to take the superscripted

David, Joffre and Mark thank's for all the comments. All my first typography projects I inclued this two glyphs in the same size and alignment but recently I have change the registered glyph to a superscript character (after I read "The Elements of Typography Style" ). I put this question because I didn