Most Helpful Guy
Generally there are some things that say 'suit coat' more than sports jacket. Most of them are more tendencies then rules. The giveaway in your case that you were wearing an orphaned suit jacket would be the buttons. On a solid color blazer you're not going to have blue buttons. Most commonly you'd have metallic ones on a blazer. If you want to use it both on its own and as part of the suit you could consider replacing all the buttons with ones made from brown horn. Horn sort of works both as a suit (slightly less formal) and as a sport coat/blazer button.