I assume that you are asking about a Notice of Opposition filed in the U.S. Patent and Trademark Office against a trademark registration application. I offer the following pointers; this should not be taken as legal advice. The Trademark Trial and Appeal Board (TTAB) will hear the opposition, so you must follow their regulations as to font size and style. The basic rules are set out in 37 CFR 2.126, which specifies a minimum of 11-point type that is double spaced. See http://www.uspto.gov/...