Is there any indication whether a rune is "primary" or "secondary" for a specific color, from the rune page in the store? Obviously that word itself doesn't matter, and just the stats themselves do, but I'm just not seeing any indication of whether the runes in the store are the "ideally suited" runes of a given type/color.
Unfortunately, the only in-game way to determine numerical ranking is by comparing the values of the mark/seal/glyph directly (A secondary stat will be lower for an equivalent tier rune when compared to a primary stat).
It sucks, but it is what it is.
Fortunately, fanmade data exists which can alleviate this unfortunate design oversight. For this, I point you directly at this page on the League of Legends Wiki.